genetics + mendel Flashcards
A phenotypic ratio of 3:1 in the offspring of a mating of two organisms heterozygous for a single trait is expected when:
the alleles segregate during meiosis
Mendel first proposed that alleles segregate from one another during the formation of gametes.
To identify the genotype of yellow-seeded pea plants as either homozygous dominant (YY) or heterozygous (Yy), you could do a test cross with plants of genotype _______ and it would be called a ___
A cross with the homozygous recessive (yy) is a test cross. If the parent of unknown genotype is heterozygous (Yy), half of the offspring will have the recessive trait. The unknown genotype could also be determined by a cross with a known heterozygote (Yy).
A phenotype ratio of 9:3:3:1 in the offspring of a mating of two organisms heterozygous for two traits is expected when:
the gene pairs assort independently during meiosis
Which of the following genetic crosses would be predicted to give a phenotypic ratio of 9:3:3:1?
A. SSYY x ssyy
B. SsYY x SSYy
C. SsYy x SsYy
D. SSyy x ssYY
E. ssYY x ssyy
SsYy x SsYy
The dihybrid cross was invented by Mendel to discover the independent assortment of alleles during gamete formation.
The expected phenotypic ratio of the progeny of a SsYy x ssyy test cross is:
1:1:1:1.
Gametogenesis:
the production of germ cells by germ-line cells in the gonads
- differentiation.
How the daughter cells become sperm
what happens to sperm cell during differentiation?
- Form microtubules. Make flagellum. Pack all their mitochondria into the blob at the top right below the 23 chromosomes. Lose all their cytoplasm. Have just a bag ‘head’ with all their chromosomes. And have a tiny lysososme in there too.
does differentiation involve division?
no- just rearrangement
Female oogenesis
process of oocyte to an egg- like female meiosis
what happens with female eggs from birth to puberty?
females are born with 500,000-1 million eggs. ‘primary oocytes’ in the ovaries. Beginning to condense their chromosomes- and then they freeze. Arrested in prophase I from birth – puberty. At puberty, when period begins: 10-12 oocytes wake up for ovulation.
when does meiosis happen in oogenesis?
at time of ovulation, 1 winning egg is released- as it escapes the ovary, the first meiotic division occurs
what happens during the first meiotic division of oogenesis- how do you go from 2 potential egg cells to 1?
one cell gets all the cytoplasm and the other cell gets 23 chromosomes but NO cytoplasm. That ‘polar body’ fades away, nothing happens
in oogenesis, after the first meiotic division, what happens to the egg cell?
the one that got the cytoplasm travels down the fallopian tube. If it encounters a sperm, then it goes through a second meiotic division
the winning egg- how many chromosomes does it have just before it meets a sperm?
if it goes through meiosis 2, then it sheds half of sister chromatids- forms a SECOND polar body, also discarded. Now, 23 chromosomes, and a little sperm head meets it
what’s the signal for the second division of the egg
Sperm = signal for second division
what happens when the sperm meets the egg?
The sperm dumps its chromosomes into the egg; 23 + 23; new nucleus formed with 46 chromosomes. At this point: fertilized egg has now become a diploid zygote.
what’s an ovum?
unfertilized egg
fungus- what’s its life cycle?
- Entire life cycle spent haploid, not diploid, except for brief zygote moment.
what’s unique about fern reproduction?
- FERNS, have both haploid spores and haploid roots, and then have diploid ferns.
heterochromia
one blue eye one brown eye
who determines the sex of the child?
male
- Standard genetic protocol:
parent x parent -> first filial generation (F1) . self cross -> F2: second filial generation. 3:1 ratio dominant to recessive in F2’s.
true breeding
homozygous. 2 copies of each chromosome both with the same gene, aka : SS x ss.
