Topic 1 Genes to Genomics

Heterozygote means different versions of the same _____

gene

Assumed blending inheritance is

average of parental phenotypes

most of out understanding came from plant/animal breading in the form of

artificial selection

Genome

the entire sequence of DNA in an organism

Locus

a general region of interest in a gnome

Gene

generally a specific region of the genome that codes for a particular protein - at a specific locus

allele

a specific sequence of a gene, generally to compare between alleles of a single gene

Homozygote

in diolpods, where both copies of a gene are the same allele - a genotype

Heterozygote

in diploids, where both copies of a gene are different alleles - a genotype

Genes and alleles and the recipe analogy

A gene is like a recipe, and alleles are variations of that recipe

non functional alleles are also called

non alleles

most times locus = _____

gene

gene doesn’t = ______

allele

Genotype

the genetic sequence of interest

Phenotype

the physical/cellular/protein results of a genotype and environmental effects

Phenotype example is

When a humans skin turns darker in the summer , no genes are changed, only due to environmental factors

Dominant

alleles phenotype appears in both homozygotes and heterozygotes

Recessive

alleles phenotype only evident in homozygotes

P/P0

Parental Cross (homozygotes)

True breeding refers to which generation?

P0

F1

First generation offspring/hybrid - heterozygotes

shows dominant phenotype and genotypes hidden

F2

Second generation offspring/hybrids

Shows all possible phenotypes and can infer all genotypes

Monohybrid cross

looks at single trait/gene

Dihybrid cross

looks at 2 traists/genes

Test cross

Determines unknown genotype by crossing with a homozygous recessive

Which of the following is not a phenotype?

Black hair

Yellow peas

Smelly farts

Misfolded proteins

None of the above

None of the above because phenotypes are the results of a genotype and enviro effects (need more info for answers)

Why were Mendel peas a good choice or organism with lucky traits?

• High # of progeny and fast growing, easy to control

• Different varieties were readily available

• Easily distinguishable states

• No linkage

  • traits controlled by single genes

Mendels approach #1

• designed crossed carefully and kep detailed records

• Counted # of offspring and traits (math)

• Kept track of generations

  • Asked specific questions and made testable predictions from results

Mendels approach #2

• Created “true breeding” lineages

  • USed good controls

Selfing plants is easy to make true breeding lineages because animals are to much

work

Mendels experiment #1

• monohybrid cross of 2 varieties of true breeding plants that differed in 1 character

  • only 1 phenotype appears in the F1 dominant

  • no info about genotype

F2 shows all possible _______ from combinations of _________

phenotypes, genotypes

Which generation has least phenotypic variation

F1

F2 has mostly a _:_ ratio

3:1

in F2 generation information on recessive gene is

not lost

RR

homozygote

Rr

Heterozygote

R_

Unknown

+/+ or vg/vg

indicated wildtype NOT dominance (will be told dominance prior)

wildtype is

what tells you what is most common in the wild

Mendels conclusions

• the is a difference between a trait (phenotype_ and the info for the trait (genotype

• round seeds is dominant phenotype

  • Wrinkled seeds is recessive

Mendels conflusions 2 - modern technology

1. Alternative versions of genes (different alleles) account for variation in inherited characteristics

2. Diploid organisms inherit 2 alleles, one from each parent

3. if 2 alleles are different, one may be dominant

4. Each haploid gamete carries only 1 allele of a given trait because of segregation in Meiosis

Mitosis gives

2 identical daughter cells

Meiosis gives

4 different cells

independent (random) segregation

2 chromosome copies split up

Law of segregation

• alleles of a gene separate independently (randomly) from each other during transmission from parent to offspring (during meiosis)

• the dominant phenotype appears at 100% in the F1 hybrid generation

Law of segregation ratios Phenotype: ______ and genotype ______

Phenotype is 3:1 and genotype is 1 (Homo dom), 2 (hetero), 1 (Homo Rec)

Test cross needs

a true breeding recessive (tester yy) and unknown

What is the expected genotype ratio of an F1 monohybrid cross?

1:2:1

In mendelian crosses phenotypes are _________

independent

For every mendelian character, one trait is _____ and one is _________

dominant, recessive

a dihybrid cross = 2 _____ crosses

monohybrid

Semi colon indicates separate ______

genes

the dash represents

different versions of the same allele

Dihybrid involves 2 traits. 2 dominant and 2 recessive _______ possible

phenotypes

Dominance relationships are not ______ by other genes

altered

Dihybrid cross set up with peas

• Start with P0 with true breedings of each variation

• F1 hybrids are all hetero at 2 genes

• F2 has a mixture of parental and random variations

Random segregation will lead to ___ possible gamete combinations

4

what is the phenotypic proportions in F2 of a dihybrid cross

9:3:3:1

Double dominant

carries both dominant alleles for both genes

Single dominant

carries 1 dominant allele for one of the traits, and recessive for the other

Double recessive

Carries both recessive alleles for both traits

Parental phenotypes

look exactly like the parents in the P0 generation

Yellow and round, green and wrinkled

Recombinant Phenotypes

Phenotypes not in parental P0 generation

Yellow, wrinkled, green round

Does the combination of alleles in the P0 affect the F1?

No

Does the arrangement of alleles in the P0 affect the F2?

No, there are the same number of each allele, so independent assortment and segregation produce the same F2

But it does change the parental and recombinant genotypes

For a mendelian dihybrid cross, if we only talk about colour what will the ratio be? (for peas)

3:1

How to find the probability of 2 independent events happening together

probability of 1 event multiplied by the probability of the second event

the additive rule

If the events A and B are independent, the probability that only one of the them occurs if (AorB)

If 2 events do not overlap in the sample space, they are said to be ______ _______

mutually exclusive

Most common in genetics is if in doubt ______

multiply

What is the probability of a mouse having the genotype ddttgg? P(dd)= 1/2, P(tt)=1/4, P(gg)=1/8

1/64

How many gamete genotypes can form from a cat with a genotype of AabbCCDD

2

How many gemete (sperm/eggs) genotypes can form from a cat with this genotype

8

How to find genotype combinations

total possible allele combinations (Aa BB) is 2 for the As and 1 for the Bs so 2×1=2

how is 2n used for genotype

n is the number of segregating loci

What is the prob of producing a kitten w their mothers genotype? Mom: Aa BB Cc Dd, Dad: aa bb CC DD

none because dad only has small bs and one B has to come from both parents

how many pairs of chromosomes are there in humans

23 pairs (46 total)

how many autosomes

22 pairs

how many sex chromosomes

1 pair (x and y) are not alike

why is mendelian inheritance more difficult for humans

cant do crosses, or punnet squares

many humans diseases are caused by mutations in a ______ gene

single

BRCA2 autosomal dominant is what disease

breast cancer

CRCA2 affects the tumor suppressor defect giving predisposition to breast and other

cancers

Recessive mutations

• most common causes of human genetic diseases

• individuals with disease are homozygous for the recessive allele

Null alleles

• recessive alleles usually lack function

  • illegible DNA

  • Fail to make product/protein

Obstacles to human genetic analysis

• incomplete family records

• small # of progeny

• Uncontrolled enviro

Wild type = ______ = healthy

normal

Affected = ______ = mutant

diseased

________ are diagrams that show the relationships among the members of a family

pedigrees

How to analyze a pedigree

1. Dominant or recessive

2. Write in genotypes

3. Follow tree and do math

Recessive traits

• may occur in individuals whos parents are not affected

• Skip generations

• occur rarely in a pedigree

• hidden in heterozygotes (carriers)

  • most likely to occur in incest families

Dominant trait pedigrees

unaffected parents cant have affected child

recessive trait pedigrees

unaffected parents can have an affected child

Dominant traits pedigrees _____ to appear in every generation

tend

Recessive traits in pedigrees tends to ____ generations

skip

if a genetic condition is rare it will be _______ in very few families in a population

present

unaffected individuals that marry into the family with the condition are likely _____ for the normal allele rather than _______

homozygous, heterozygous

Albinism pedigree

1. Mark albinos as homozygous recessive

2. Parents of albino must have recessive alleles

3. Unaffected offspring must be carriers

4. Rest are unaffected

5. Recessive inheritance checks out

Zygosity

unaffected but unknown genotypes A/-