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.
Allele:
alternative forms of the gene for a particular trait. Ex: smooth and wrinkled version= 2 alleles.
heterozygous
Ss
monohybrid cross
Ss x Ss. basically crossing two of the same genotype together
T/f: only see a homozygous recessive type in F2 generation
True
Law of segregation
recessive trait is not lost- can be re-xpressed in next generation.
genotypic ratio of monohybrid heterozygous cross
Genotypic ratio: 1: 2: 1
(SS: Ss: ss)
example of a human trait that expresses only in homozygous recessive form
albinism
example of a lethal ominant gene
huntington’s disease- shows that dominant/reccesive isn’t the determination of frequency
primary oocyte is what?
diploid
secondary oocyte?
test cross
have an organism with a dominant phenotype and unknown genotype. cross with homozygous recessive individual- look at resulting genotypes of children to determine parent’s genotype
what do you know about the parent if you get a 1:1:1:1 phenotype in a test cross
ratio for a test cross in which the alleles of the two genes assort independently into gametes (BbEe × bbee
9:3:3:1
If both parents are heterogeneous for both traits the ratio of phenotypes is the ratio of 9:3:3:1.
quickly describe role of sugars in blood type
Surface of blood cell: sugars attached to proteins- facing out- gets modified with an extra sugar. serves as the receptor for either A or B type blood
difference between A, B and O blood?
- A,B have the extra sugars on their receptors and O does not
T/f:
- Only difference between A, B sugar is their R groups
True!
what is ‘eyrthroblastosis fetalis’ / Rh disease?
- Mom Rh-, baby Rh+, at birth placenta comes loose and mom’s immune system is exposed to small amount of baby’s blood. In second baby, can train her immune system to attack the Rh+ blood
- In second baby, if Rh+, her immune system can cause her baby’s blood to have immature red blood cells with a nucleus! Blood cells aren’t supposed to have nucleus.
treatment for Rh diseases?
- Treatment: test mom during 1st baby: if Rh+, inject mother with Rhogam, blocking antibodies. Masks the Rh+ from her immune system her body never attacks it. They will inject her with this every time.
- Sickle cell anemia: Mutation in ___chain
beta hemoglobin
___ of African americans are carriers of sickle cell anemia
1/12 of African americans are carriers!
product rule
- the probability of 2 independently occurring events occurring together is equal to the product of the probabilities of either event occurring alone
- Aka: getting heads twice in a row- = ½ * ½ = ¼.
how do you calculate probability of 1 abnormal child out of 3 births?
- (P+q)3 = 1 (out of 3 births)
- P is normal (3/4 probability) and q is mutated (1/4 probability)
- P3 + 3p2q + 3pq2 + q3 = 1
- term indicating 1 mutant and 2 normal: 3p^2q- 3 ways to have this
Partial dominance
- dilution effect when dominant and recessive mix): 1:2:1 phenotype & genotype ratio
- ex: red RR x white ww flower produce new color: pink flower
occurs when the phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. For example, the snapdragon flower color is homozygous for either red or white.
in what situation does Phenotypic ratio matches the genotypic ratio?
partial dominance
Co-dominance
blood type - AB
Polygenic inheritance
Many different kinds of genes which all contribute to a certain phenotype. ex: height
Sex-influenced:
- genes are not on sex chromosomes but they are affected by sex hormones of an individual
- Balding: homozygous dominant both sexes are good, heterozygous dominant (males are bald, women are good), homozygous recessive (males bald, women very thin hair)
Sex-limited:
- traits that you see only in one sex and not the other
- Male chickens have certain types of feathers that females will never have
- Even though a woman can have the homozygous recessive trait for the gene, it will not express (only will in men)
Interaction of genes- chicken example?
- When two dominant genes (that are separate—not alleles) are together, you get a new phenotype
- Rose comb is dominant to single comb and pea comb is dominant to single come. If you cross them and put rose comb and pea comb together, you can get a walnut comb where Rose and Pea dominant genes produce new phenotype
- P:3:3:1 walnut, rose, pea, single
- Both dominants contribute/interact to create same (but new) phenotype
