BIO 97 LECTURE 10 – Flashcards

An inversion heterozygote for a large inversion - A large heterozygous inversion will result in greater numbers of genes that are duplicated or deleted when crossing over occurs.

chromosome with two centromeres - When the centromere is contained within the inversion, it is neither duplicated nor deleted. ---- - chromosome with some deleted regions - completely normal chromosome - chromosome with some duplicated regions

FALSE - Loop formation allows pairing within inverted regions of homologous chromosomes regardless of whether the centromere is included in the inversion.

the smaller of the two reciprocal products of translocated chromosomes is lost -After several cell divisions, only the larger of the two translocated chromosomes remains. Its reciprocal is lost.

If one parent is a translocation heterozygote for chromosomes 14/21, a child born to this parent is as likely to have Down syndrome as he is to be normal. - Three viable zygote types are possible when fertilization occurs between one normal and one heterozygous parent. One-third has a normal chromosome complement, one-third is a carrier, and one-third has Down syndrome. ---- - It accounts for approximately 5% of all Down syndrome cases. - Heterozygous carriers of the Robertsonian translocation that causes familial Down syndrome can have children who are phenotypically normal and are not carriers of the translocation. - Heterozygous carriers of the Robertsonian translocation that cause familial Down syndrome can have children who are also carriers of the translocation.

6 -During meiosis, the Robertsonian chromosome may sort to one pole of the cell alone, with the normal copy of chromosome 14, or the normal copy of chromosome 21. The other chromosomes migrate to the opposite pole.

Homologs fail to separate during meiosis I. - ordinarily, homologs separate during meiosis I. Failure of this separation is one of the ways in which nondisjunction can occur.

two haploid gametes fuse to form a diploid cell - Fusion of haploid gametes occurs after meiosis. --- - sister chromatids separate from one another during meiosis II - one diploid cell produces four haploid cells - homologous chromosomes separate from one another during meiosis I

false - Nondisjunction during either meiosis I or meiosis II creates gametes that will generate trisomies if fertilized.

two - Nondisjunction in meiosis II produces one nullosomic gamete and one disomic gamete. The two products produced by the other meiosis I daughter cell will produce two normal haploid gametes.

Partial duplication and deletion

Paracentric inversion

monosomy XO

homologous chromosomes align during meiosis through formation of an inversion loop at synapsis.

Reduced fertility - Trivalent synaptic structures form in meiosis I. Segregation of homologs results in the production of aneuploid gametes.

pericentric inversion (the centromere is within the inverted region)

a cell that contains a multiple of the haploid (X or Y) set of chromosomes - human somatic cells and human gametes are both haploid

cells that do not contain a multiple of the haploid sets (X or Y) - monosomy: only one copy of a given chromosome in an otherwise haploid cell - trisomy: 3 copies

cause of aneuploidy; chromosomes or sister chromatids fail to disjoin during meiosis - risk increases with age - in meiosis I: produces gametes with a pair of homologous chromosomes (e.g XY) - in meiosis II: produces gametes with a pair of sister chromatids (ex. XX or YY) - ex. trisomy-X = 47, XXX (female) double-Y= 47, XYY (male) klinefelter syndrome= 47, XXY (male, sterile) turner syndrome= 45, X, (female,sterile)

most common autosamal (non-sex chromosome) aneuploidy - down syndrome= genetic disorder due to trisomy 21

interchange of genetic information between non-homologous chromosomes - a piece of one goes to another - between similar sequences on non-homo chromosomes

arise when a piece on one chromosome is translocated to a nonhomolg and there is no reciprocal event

occur when pieces of two nonhomologs switch places

fusion of two nonhomologous chromosomes

genetic rearrangement in which the order of genes is reversed in a chromosome segment - between similar sequences within a chromosome

deletions= missing chromosome segment large deletions often lethal (even in even in heterozygotes) - between similar sequences within a chromosome - between tandemly repeated sequences on homologous chromosomes

chromosome segment present in multiple copies tandem duplications : repeated segments are adjacent; often result from unequal crossing over - between tandemly repeated sequences on homologous chromosomes

the centromere is outside of the inverted region

the centromere is within the inverted region