Biology 1001A Lecture Notes - Lecture 3: Earthbound, Y Chromosome, Probability Distribution

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Lecture 10
- This course is all about evolution and evolution needs variation, it needs heritable variation, if variation
cannot be passed on to offspring then it is invisible to selection. This is why we are studying heritable
variation.
- Alternate alleles have different DNA sequences. These differences in DNA sequences between alleles
could just be do to SNPs.
- Variation is a mutation. 4 ost iportat (ells do’t ko hat type of variation they need. There
is no way for organisms to direct which mutations to suffer. But some organisms can induce variation as
by sexually reproducing instead of asexually reproducing in response to environmental stress)
5. Variation and mutations are not random (the likelihood of bps suffering a certain mutation is not
equal for all bps), but mutations are not directed.
6. Only variation that can be passed on is relevant to selection and evolution
Cotiuous ariatio is ofte otrolled y ay gees (Medel’s geius as ot lookig at these traits
because they suggested blending). Mendel is awesome because he got his results without the
knowledge of chromosomes, genes, meiosis, etc.
Alleles segregate randomly into gametes - an organism has two copies and deals one or the other to its
offspring (one of these alleles could determine the phenotype of heterozygotes dominant allele)
Monohybrid (heterozygote cross): why is the probability ½? Because its meiosis! These gametes came
from spores that were the products of meiosis in a plant.
Mendel never had to deal with sex chromosomes while working with peas, but chromosomes are
important aspect of inheritance and the inheritance pattern of genes carried on sex chromosomes is
different than if they were carried on autosomes because of sexual dimorphism around chromosome
content in males and females. The sex chromosome composition of humans (males vs. females) are the
same in fruit flies (males have XY and females have XX)
Human Sex Determination does depend on the SRY gene on the Y chromosome, but the formation of
sex-specific reproductive structures is equally likely to be encoded on autosomal chromosomes, and on
both Xs (if female) and on both X and Y (if male).
Eily has a uterus. What are the gees for akig Eily’s uterus?
1. On X chromosome from mother
2. On autosomes such as chromosome 6 or 14
3. On X chromosome from father
4. On mitochondrial chromosomes (only from father)
Sex-linkage has been illustrated by working with fruit flies in reciprocal crosses. Red eyes = normal (W+)
White eyes = mutant (W) plus sign does not mean dominant
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Document Summary

This course is all about evolution and evolution needs variation, it needs heritable variation, if variation cannot be passed on to offspring then it is invisible to selection. This is why we are studying heritable variation. These differences in dna sequences between alleles could just be do to snps. 4 (cid:373)ost i(cid:373)porta(cid:374)t ((cid:272)ells do(cid:374)"t k(cid:374)o(cid:449) (cid:449)hat type of variation they need. There is no way for organisms to direct which mutations to suffer. Co(cid:374)ti(cid:374)uous (cid:448)ariatio(cid:374) is ofte(cid:374) (cid:272)o(cid:374)trolled (cid:271)y (cid:373)a(cid:374)y ge(cid:374)es (me(cid:374)del"s ge(cid:374)ius (cid:449)as (cid:374)ot looki(cid:374)g at these traits because they suggested blending). Mendel is awesome because he got his results without the knowledge of chromosomes, genes, meiosis, etc. Alleles segregate randomly into gametes - an organism has two copies and deals one or the other to its offspring (one of these alleles could determine the phenotype of heterozygotes dominant allele) These gametes came from spores that were the products of meiosis in a plant.

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