chapter 3 Flashcards

Question

Meiosis and Mendel’s Laws

Answer 1

Alleles segregate during recombination AND when homologs separate The arrangement of homologs during metaphase I dictates the independent assortment of multiple genes

Answer 2

Oogenesis & Spermatogenesis

Answer 3

1 egg cell per division, four sperm cells per division Millions of sperm are produced daily; one egg is produced each menstrual cycle

Answer 4

Primary oocytes are established in females during embryonic development (~20 weeks after conception) - About 7 million primary oocytes are present at this time * Number decreases to 1-2 million by birth * By puberty the number decreases to 60 000 – 80 000 * About 500 mature oocytes are produced during a woman’s life

Answer 5

Nettie Stevens was the first to observe sex chromosomes * studied chromosomal differences in male and female beetles * She found diploid female cells contained 20 large chromosomes, but diploid cells from male beetles contained 19 large chromosomes and 1 small chromosome * This small chromosome came to be known as a Y chromosome

Answer 6

Morgan and colleagues discovered the white- eyed mutant * This mutation was found to be recessive to the red-eyed phenotype (wild-type) the white-eyed allele was found on sex chromosomes * More specifically, the white-eyed phenotype is X-linked, meaning the allele is located on the X chromosome

Answer 7

* All F1 males had white eyes F2 progeny were an equal mix of white-eyed males, white-eyed females, wild-type males, wild-type females These two crosses demonstrated that males are more prone to expressing the recessive phenotype because it is on the X chromosome and males only have one X chromosome

Answer 8

having one allele (male flies in morgans cross)

Answer 9

X:A ratio system Ratio of X chromosomes to autosomes determines sex * Y chromosome does not determine sex Sisterless protein is expressed from the X chromosome Deadpan protein is expressed from autosomes * When two sisterless proteins dimerize (connect) at high concentration, female flies are produced * When deadpan proteins dimerize with sisterless proteins at high concentration, male flies are produced * Two X chromosomes = higher expression of sisterless = higher chance of sisterless proteins dimerizing * One X chromosome = lower expression of sisterless = higher chance of deadpan dimerizing with sisterless proteins

Answer 10

Z/W system * Females have ZW chromosomes (females hemizygous in these animals) * Males have ZZ chromosomes In animals where females have two different sex chromosomes * Called Z/W to avoid confusion with X/Y sex determination

Answer 11

5 pairs of sex chromosomes 5 XY = male 5 XX = female

Answer 12

gene called sex determining region of Y (SRY) Males: * Usually: XY * Rarely: XXY, XYY, XYYY Females: * Usually: XX * Rarely: XO, XXX, XXXX

Answer 13

colour blindness Only expressed in women that are homozygous recessive It is common for men to inherit the condition directly from their heterozygous mothers (carriers)

Answer 14

rare X-linked dominant disorder in humans * It leads to a large increase in the number of hair follicles on the body, and affected males and females have more body hair than normal

Answer 15

all daughters inheriting condition from father

Answer 16

females have twice as many X chromosomes as males * This creates differences in the “dosage” (expression) of X-linked genes * Females could have twice as much protein expressed from their X- chromosomes * Mechanisms exist to compensate for these differences in sex chromosome number and it is called dosage compensation

Answer 17

X-inactivation occurs early in embryonic development * Any given cell inactivates either the maternally inherited X chromosome or the paternally inherited X chromosome on a random basis * This means all cells in a female’s body are mosaics of two cell types: one expresses the maternal X chromosome, the other expresses the paternal X chromosome

Answer 18

Mosaicism or "lines of blaschko" are due to different patches of skin that are descended from embryonic cells with different X-chromosomes being inactivated

Answer 19

In cats, the X chromosome carries a gene responsible for coat color * One allele specifies a black color; the other an orange color * X inactivation in heterozygous females leads to a pattern of orange and black patches that is unique to each individual