AP Biology Unit 5: Heredity (copy)

-Mitochondrial

-Y-Linked

-Sex-Linked Dominant

-Sex-Linked Recessive

-Autosomal Dominant

-Autosomal Recessive

• Mother who is affected passes it down ALL of her kids

• Only passed down by females who are affecte

• Father who is affected passes it down to all of his sons

• affected father (X^AY) passes it down to all of his daughters(X^AX^_)

• can show as more common in males (X^aY)

• affected female(X^aX^a) passes it down to all of her sons(X^aY)

• usually in every generation

• 2 affected parents(heterozygous: Aa) can have unaffected kid(aa)

• can skip generations

• if both parents affected(aa), ALL kids are affected(aa)

• 2 unaffected parents(Aa/carriers) can have affected kid(aa)

Meiosis is how gametes(sex cells) are made. Egg and sperm cells are gametes.

-Replication occurs during the S phase. Each chromosome is duplicated. Each duplicated chromosome has two identical sister chromatids.

-This roughly doubles the amount of DNA in the cell, but the number of chromosomes should stay the same.

-2 chromosomes per pair

(2n): n= # of pairs

Half the initial amount of initial chromosomes

2 - Meiosis 1 & Meiosis 2

Meiosis 1 result: 2 haploid cells

Meiosis 2 result: 4 genetically unique haploid daughter cells

• Homologous chromosomes pair up and synapsis occurs (homologous chromosomes form a tetrad and align gene by gene)

• *crossing over: increases genetic variation and happens 2-3 times per homologous pair

• homologous pairs line up at the metaphase plate

• *independent assortment: random combinations of which chromosome ends up on which side —> increases genetic variation

Mendel's law of independent assortment states that the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.

• The spindle(fibers) apparatus helps move chomosomes towards opposite ends of the cell(separates homologous pairs)

• Sister chromatids stay connected and move towards the poles

• Two cells are formed

• Each cell is now haploid

• spindle apparatus forms and you can see chromosomes

• Chromosomes line up individually at the metaphase plate

• Sister chromatids separate and individual chromosomes move to opposite ends of the cell

• chromosomes have moved to opposite ends of the cell

• nuclei reappear

• cytokinesis occurs

• 4 genetically unique haploid daughter cells

During fertilization, an EGG cell and a SPERM cell(each produced during meiosis) come together. Because each egg and sperm is different, as a result of INDEPENDENT ASSORTMENT and CROSSING OVER, each combination of egg and sperm is unique. In humans, there are about 70 million (223×223) possible combinations-and this is all without considering crossing over!

1) homologous pairs

2) sister chromatids

3) diploid, haploid, 1

4) gametes

1. synapsis and crossing over

2. alignment of homologous pairs at the metaphase plate

3. separation of homologs

Increases genetic diversity

At metapahse 1, paired homologous chromosomes are positioned on the metaphase plate, rather than individual replicated chromosomes(mitosis). This allows independent assortment of maternal and paternal chromosomes, which increases genetic diversity.

At anaphase 1, duplicated chromosomes of each homologous pairs separate, but the sister chromatids of each duplicated chromosome stay attached

1) Crossing Over

2) Independent Assortment

3) Random Fertilization

-Prophase 1: exchange of genetic material on homologous chromosomes occurs. All four chromatids that male up the tetrad are different because of crossing over. In metaphase 2, when sister chromatids separate, each chromatids is unique, increasing variation.

In metaphase 1, when the homologous chromosomes are lined up on the metaphase plate, they can pairs up in ANY combinations with any of the homologous pairs facing either pole. This means that there is a 50% chance that a particular daughter cell will get a maternal chromosome or a paternal chromosome from each of the homologous pairs.

*Maternal and paternal Genes divided randomly during meiosis

Because each egg and sperm is different, as a result of independent assortment and crossing over, each combination of egg and sperm is unique.

The failure of one or more pairs of homologous chromosomes or sister chromatids to separate properly during nuclear division, usually resulting in an abnormal distribution of chromosomes in the gametes that are formed.

• homologous chromosomes fail to separate properly during meiosis 1 —> affects all daughter cells

• At the end of meiosis, 2 cells have an extra chromosome(n+1), 2 cells are missing a chromosome(n-1)

• sister chromatids fail to separate properly during Meiosis 2

• affects 2 cell, other 2 cells are normal

• 1 cell has an extra chromosome(n+1), 1 cell is missing a chromosome(n-1), 2 cells have normal number of chromosomes(n)

Triploid —> infertile bc you can’t pairs up bc there’s triplets —> can’t line up in homologous pairs during meiosis in order to be separated during anaphase

refers to some of the changes in an organism’s behavior, morphology, and physiology in response to a unique/[change in an] environment.

diet, temperature, pH, oxygen levels, humidity, light cycles, presence of mutagens

Environment can affect the the expression of genes and the production of proteins that “make” the traits. (i.e. temperature can affect whether eggs in some species develop as males or females)

• difference between O/E due to chance

• accept null hypothesis

• follows independent assortment

• difference between O/E not due to chance

• genes may be on same chromosome(linked)

• reject null hypothesis

• does NOT follow independent assortment

Incomplete dominance is a form of Gene interaction in which both alleles of a gene at a locus are partially expressed, often resulting in an intermediate or different phenotype.

-ex. Red (RR) x White(Rr) = Pink(Rr)

Codominance, as it relates to genetics, refers to a type of inheritance in which two versions (alleles) of the same gene are expressed separately to yield different traits in an individual.

-ex. Red(RR) x White(rr) = Red/White(Rr)

*can use the recombination frequency to determine how relatively far apart the genes are located

Recombination frequency (RF) = (Recombinants/Total offspring) x 100%

According to independent assortment, the inheritance of one gene/trait is independent to the inheritance of any other gene/trait.

• independent assortment happens only if genes for Alleles are on different homologous chromosomes.

• Independent assortment is due to the random orientation of Paris of homologous chromosomes in Meiosis 1.

Independent Assortment will not occur if two genes are located on the same chromosome(linked genes)

When genes are “linked” on the same chromosome…

• the closer together they are, the LESS likely they will experience recombination or crossing over between them

• the FURTHER APART they are on the same chromosome, the MORE likely they will experience recombination or crossing over between them

Happens when genes are located on DIFFERENT homologous chromosomes

• When we do Punnet Square, we are modeling the independent assortment of alleles during meiosis and fertilization. This assumes two things:

  • The genes are NOT linked

  • The genes are found on different sets of homologous chromosomes

  • Crossing over between the genes DOES NOT happen

• This, if you run a CHI-SQUARE test, the results that you observed in the cross SHOULD follow the expected phenotypic ratios from the punnet Square(accepted the null hypothesis)

Linked Genes - Genes are located on the same chromosome

• if the results of the cross DO NOT reflect the expected phenotypic ratios from the Punnet Square(rejected the null hypothesis), then it is POSSIBLE that…

  • the genes ARE linked

  • They are found(relatively close together) on the same chromosome

  • Crossing over between genes can happen

• We use crossing over frequency to determine how close together on the chromosome these genes may be

  • the MORE frequently they cross over(higher recombination frequency), the farther apart they are

  • the LESS frequently they cross over(lower recombination frequency), the closer together they are on the same chromosome