Biology 1 Chp 11 WORKSHEETS Introduction to Genetics – Flashcards
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The scientific study of heredity is called...
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genetics
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What is true about Gregor Mendel's peas?
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- When pollen fertilizes an egg cell, a seed for a new plant is formed. - Pea plants normally reproduce by self-pollination
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What does it mean when pea plants are described as being true-breeding?
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If the plants are allowed to self-pollinate,m they would produce offspring identical to themselves.
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To preform his experiments, how did Mendel prevent pea flowers from self-pollinating and control their cross-pollination?
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He cut away the pollen-bearing male parts of a flower and dusted that flower with pollen from another plant.
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genes
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chemical factors that determine traits
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hybrids
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the offspring of crosses between parents with different traits
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traits
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specific characteristics that vary from one individual to another
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alleles
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the different forms of a gene
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State the principle of dominance.
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Some alleles are dominant and others are recessive
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TRUE of FALSE: An organism with a recessive allele for a particular form of a trait will always exhibit that form.
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FALSE
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Name the traits controlled by dominant alleles in Mendel's pea plants.
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tall & yellow
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How did Mendel find out whether the recessive alleles were still present in the F1 plants?
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He allowed the F1 plants to produce an F2 generation by self-pollination
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About one fourth of the F2 plants from Mendel's F1 crosses showed the trait controlled by the _____________ allele.
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recessive
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What is true about Mendel's explanation of the results from his F1 cross?
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- Mendel assumed that a dominant allele had masked the corresponding recessive allele in the F1 generation. - At some point, the allele for shortness was segregated, or separated, from the allele for tallness.
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What are gametes?
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the sex cells
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In the following F1 generation, what represent the dominant allele and which represents the recessive allele? Tt x Tt
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T = dominant allele t = recessive allele
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The likelihood that a particular event will occur is called...
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probability
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What is the probability that a single coin flip will come up heads?
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50%
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TRUE or FALSE: The past outcomes of coin flips greatly affect the outcomes of future coin flips.
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FALSE
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Why can the principles of probability be used to predict the outcomes of genetic crosses?
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The way in which the alleles segregate is completely random, like a coin flip.
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How do genetics use Punnett squares?
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Punnett squares can be used to predict and compare the genetic variations that will result from a cross.
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genotype
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genetic makeup of an organism
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homozygous
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organism that have two identical alleles for a particular trait (TT or tt)
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phenotype
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physical characteristic of an organism (tall)
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heterozygous
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organisms that have two different alleles for the same train (Tt)
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TRUE or FALSE: Homozygous organisms are true-breeding for a particular trait.
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TRUE
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TRUE or FALSE: Plants with the same phenotype always have the same genotype.
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FALSE
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What is true about probability and segregation?
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- The F2 ratio of tall plants to short plants produced in a cross between two hybrid tall pea plants (Tt) is 3 tall plants for every 1 short plant. - Mendel observed that about 3/4 of the F2 offspring showed the dominant trait. - Segregation occurs according to Mendel's model.
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In Mendel's model of segregation, what was the ratio of tall plants to short plants in the F2 generation?
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3:1
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TRUE or FALSE: Probabilities predict the precise outcome of an individual event.
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FALSE
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How can you be sure of getting the expected 50 : 50 ratio from flipping a coin?
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You must flip the coin many times.
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The __________ the number of offspring from genetic cross, the closer the resulting numbers will get to expected values.
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larger
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TRUE or FALSE: The ratios of an F1 generation are more likely to match Mendelian predicted ratios if the F1 generation contains hundreds or thousands of individuals.
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TRUE
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probability
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likelihood that a particular event will occur
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Punnett square
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diagram showing the gene combinations that might result from a genetic cross
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homozygous
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term used to refer to an organism that has two identical alleles for a particular trait
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heterozygous
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term use to refer to an organism that has two different alleles for the same trait
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phenotype
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physical characteristics of an organism
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genotype
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genetic makeup of an organism
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independent assortment
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independent segregation of genes during the formation of gametes
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incomplete dominance
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situation in which one allele is not completely dominant over another
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codominance
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situation in which both alleles of a gene contribute to the phenotype of the organism
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multiple alleles
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three or more alleles of the same gene
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polygenic trait
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trait controlled by two or more genes
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homologous
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term used to refer to chromosomes that each have a corresponding chromosome from the opposite-sex parent
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diploid
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term used to refer to a cell that contains both sets of homologous chromosomes
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haploid
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therm used to refer to a cell that contains only a single set of chromosomes and therefore only a single set of genes
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meiosis
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process by which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell
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tetrad
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structure containing 4 chromatids that forms during meiosis
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crossing-over
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process in which homologous chromosomes exchange portions of their chromatids during meiosis
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gene map
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diagram showing the relative locations of each known gene on a particular chromosome
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In a two-factor cross, Mendel followed _________ different genes as they passed from one generation to the next.
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two
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Write the genotypes of the true-breeding plants Mendel used in his two-factor cross. Phenotype: a. round yellow peas b. wrinkled green peas
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Genotype: a. RRYY b. rryy
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What best describes the F1 offspring of Mendel's two-factor cross.
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Heterozygous dominant with round yellow peas
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TRUE or FALSE: The genotypes of the F1 offspring indicated to Mendel that genes assort independently.
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FALSE
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How did Mendel produce F2 offspring?
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He crossed F1 plants to each other.
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What phenotypes would Mendel expect to see if genes segregated independently?
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- round and green - wrinkled and yellow
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What did Mendel observe in the F2 offspring that showed him that the alleles for seed shaped segregate independently of those for seed color?
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He observed F2 offspring that had combinations of phenotypes — and therefore combinations of alleles — not found in either plant.
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What were the pheonotypes of the F2 generation that Mendel observed?
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seeds that were round and yellow, wrinkled and green, round and green and wrinkled and yellow
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What was the ratio of Mendel's F2 generation for the two-factor cross?
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9 : 3 : 3 : 1
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State Mendel's principle of independent assortment.
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Genes for different traits can segregate independently during the formation of gametes.
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What is true about Mendel's principles?
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- The inheritance of biological characteristics is determined by genes that are passed from parents to their offspring. - The copies of genes are segregated from each other when gametes are formed. - The alleles for different genes usually segregate independently of one another.
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When two or more forms of the gene for a single trait exist, some forms of the gene may be _________ and others may be _________.
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- dominant - recessive
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TRUE or FALSE: All genes show simple patterns of dominant and recessive alleles.
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FALSE
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DESCRIPTION: One allele is not completely dominant over another. The heterozygous phenototype is somewhere in between the two homozygous phenotypes.
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TYPE: Incomplete Dominance EXAMPLES: Flower color in four o'clock plants
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DESCRIPTION: Both alleles contribute to the phenotype of the organism.
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TYPE: Codominance EXAMPLES: Black and white feather color in certain varieties of chickens.
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DESCRIPTION: Genes have more than two alleles
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TYPE: Multiple Alleles EXAMPLES: Coat color in rabbits, blood type in humans, eye color in humans
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DESCRIPTION: Two or more genes control a trait
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TYPE: Polygenic Traits EXAMPLES: Eye color in fruit flies, skin color in humans
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List three criteria Thomas Hunt Morgan was looking for in a model organism for genetic studies.
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a. small in size b. easy to keep in the laboratory c. able to produce large numbers of offspring in a short time
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TRUE or FALSE: Mendel's principles apply not just to pea plants but to other organisms as well.
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TRUE
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Characteristics are determined by interaction between genes and the...
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environment
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List the two things the Mendel's principles of genetics required in order to be true.
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a. Each organism must inherit a single copy of every gene from both its parents. b. When an organism produces its own gametes, those two sets of genes must be separated from each other.
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What does it mean when two sets of chromosomes are homologous?
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Each of the chromosomes in the set from the male parent has a corresponding chromosome from the female parent.
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What are ways to describe a diploid cell?
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- 2N - contains two sets of homologous chromosomes
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What is the number of chromosomes in a haploid Drosophila cell?
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4
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Why is meiosis described as a process of reduction division?
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The number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.
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What are the two distinct divisions of meiosis?
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a. Meiosis I b. Meiosis II
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TRUE or FALSE: The diploid cell that enters meiosis becomes 4 haploid cells at the end of meiosis.
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TRUE
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How does a tetrad form in prophase I of meiosis?
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when each chromosome pairs with its corresponding homologous chromosome
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What is the number of chromatids in a tetrad??
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4
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What results from the process of crossing-over during prophase I?
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When homologous chromosomes in tetrads exchange portions of their chromatids, alleles are exchanged between the homologous chromosomes to produce new combinations of alleles.
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What is true about meiosis?
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- During meiosis I, homologous chromosomes separate. - During anaphase II, the paired chromatids separate.
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Describe this Product of Meiosis: eggs
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Haploid gametes produced in females
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Describe this Product in Meiosis: sperm
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Haploid gametes produced in males
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Describe this Product in Meiosis: polar bodies
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Cells produced in females that do not participate in reproduction
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What is true about mitosis and meiosis?
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- Mitosis begins with a diploid cell. - Meiosis begins with a diploid cell
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Compare the processes of mitosis and meiosis.
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...
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TRUE or FALSE: Thomas Hunt Morgan discovered that some genes violated the principle of independent assortment.
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TRUE
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Morgan grouped the Drosophila genes that were inherited together into four ____________ groups.
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linkage
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List the two conclusions that Morgan made about genes and chromosomes.
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a. Each chromosome is a group of linked genes. b. Chromosomes assort independently, not individual genes.
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Why didn't Mendel observe gene linkage?
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Six of the seven genes he studied are on different chromosomes. The two genes on the same chromosome are so far apart that they also assort independently.
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Explain why two genes found on the same chromosome are not always linked forever.
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Crossing-over during meiosis sometimes separates genes that had been on the same chromosome onto homologous chromosomes.
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The new combinations of alleles produced by crossover events help to generate genetic...
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diversity
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TRUE or FALSE: Genes that are closer together are more likely to be separated by a crossover event in meiosis.
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FALSE
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What is a gene map?
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It shows the relative locations of each gene on a chromosome.
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How is a gene map constructed?
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It is constructed by using recombination rates, which measure the frequencies of crossing-over between genes.
