ppt
40
Housekeeping o Finishing Chapter 2, moving onto Chapter 3 today o Use book for other example problems o Homework: 2a-albino mouse:AAbbcc o Biology in South India seminar o Tonight, 7pm Sc278 o Lab o Read ahead and will go fast! o Don’t forget your $3! DUE THIS WEEK!
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Transcript of ppt
Housekeeping
o Finishing Chapter 2, moving onto Chapter 3 todayo Use book for other example problems
o Homework: 2a-albino mouse:AAbbcc
o Biology in South India seminaro Tonight, 7pm Sc278
o Labo Read ahead and will go fast!o Don’t forget your $3! DUE THIS WEEK!
Multifactorial traits
> 1 gene
EnvironmentModifier genes
Expression and penetrance
Alleles from differentgenes complement
each other
One allele from one gene masks another
allele from another gene
Epistasis
Mutant alleles at more than one gene
can result in the same phenotype
Alleles of different genes interact to
create different phenotypes
Step 1
Step 2
Hear
Enzyme A
Enzyme B
Gene A
Gene B
Mutant alleles at Gene A or B can result in
the same phenotype: DEAF
A-
B-
2 parents are deaf. Is there deafness a result of mutations in the same gene
(i.e. they both have a mutation in gene A) or are the mutations in different
genes (i.e. one in gene A and one in gene B)?
Complementation testing
Black filled: deaf
ANALYZE THE OFFSPRING!
What might their offspring look like if the mutation is at
different genes? The same gene?
Complementation
Figure 2.15a
Noncomplementation
Figure 2.15b
Step 1
Step 2
Hear
Enzyme A
Enzyme B
Gene A
Gene B
A-
B-
Alleles from differentgenes complement
each other
One allele from one gene masks another
allele from another gene
Epistasis
Heterogenous trait
Mutant alleles at more than one gene
can result in the same phenotype
Alleles of different genes interact to
create different phenotypes
How do we determine if one or multiple
genes are involved??
Multifactorial traits
> 1 gene
EnvironmentModifier genes
Expression and penetrance
Expression and penetrance:
Retinoblastoma
o Single gene mutationo only see cancer in 75% of people with this
mutation! (Penetrance-incomplete)o Some people only have cancer in one eye,
while others in both (Expressivity-variable)
Key terms:
o Penetrance: occurance of altered phenotype
o Expressivity: at what degree does the altered phenotype occur
Expression and penetrance
o Scenario: A son is born and his father and grandfather have both had heart troubles. After genetic analysis, it is determined that the son is also prone to heart disease. The doctors say its occurrence and/or severity of the heart disease can be prevented by a healthy diet and exercise
Penetrance: occurrence of heart disease (incomplete)
Expression: severity of heart disease (variable)
Modifier genes
o Some genes don’t contribute equally to the phenotype
o Gene modifies the phenotype but not equally in all situations
Environment
o Environmental changes affect phenotype o Temperature, sunlight, chemical exposure
(smoking), diet and exercise, environmental changeso conditional mutant, conditional lethalo Phenocopy
Single gene inheritance variations
Multifactorial traits
Breeding and domestication
Artificial selection of traits
Farmer Old McDonald has a dairy farm and is trying to get the optimal
milk supply from his herd by breeding his best milkers. Daisy normally supplies 5 L per day.
However, upon several matings, the female offspring supply a huge
spectrum of milk (2, 3, 5, and 9 L of milk). Being a geneticist, what might
you conclude is happening?
Continuous/quantitative trait
o Polygenic: more than one gene is involvedo Height, skin color, weight, milk production
Mendel’s predictions1. One gene determines one trait
>1 gene can affect phenotype!Multifactorial traits (penetrance and expressivity)
2. We have different alleles for each genemultiple alleles exist for one gene
3. We have 2 alleles for each gene in our body
4. Some alleles may be dominant, some recessiveincomplete/complete dominance
5. Law of Segregation Our 2 alleles separate during meiosis
6. Law of independent assortmentAlleles segregate independently during meiosis
Microscopy
o Sperm mates with egg
o Chromosomes are in cells
o Chromosomes are inherited
o Sex chromosomes exist
Chromosome Theory of Inheritance
o Genes are located at loci on chromosomeso Chromosomes are what undergo segregation and
independent assortment
Karyotype
Who we are depends on:
1. What type of genetic material
we get2. How much
genetic material we get
How do we inherit the appropriate amount
of genetic material?
Sexual reproduction
Gametes
Somatic Cells
o What is a gamete?o Reproductive cello Single set of chromosomes: HAPLOID
o What happens during fertilization?o 2 haploid cells (gametes) come togethero Zygote: DIPLOID
Sexual reproduction
Sexual reproduction
Gametes
Somatic Cells
23 + 23 46 46
o What is a somatic cell?o Any cell other than sperm or ovumo DIPLOIDo One chromosome from each parent
How do we create gametes?
How do we maintain
somatic cells?
Key Terms
Figure 3.5
Termso Chromosome: piece of DNA (string of nucleotides)
o Chromatin: chromosome + proteins
o Chromatid: condensed chromatin
o Sister chromatids: Identical chromosomeso Occurs when one chromosome gets replicated for
mitosis or meiosis
o Homologous chromosomes: similar chromosomeso Normally contain same genes (may have different
alleles)
Homologous/nonhomologous chromosomes
Genetic makeup of organisms
Organism # homolog. Chrom. pairs Total
Humans 23 46
Drosophila melanogaster
Drosophila obscura
4 8
5 10
Peas (that Mendel used) 7 14
Goldfish 47 94
Dogs 39 78
Peanuts
Strawberries
4x
8x
Who’s male, who’s female?
Table 3.1
How do we create gametes?
How do we maintain
somatic cells?
Growth phase
Arrested Growth phase
Figure 3.7
What are the steps of mitosis?
What is the relevance of each step?
“Mitosis Madness”
By the students of St. Olaf College in Barb May’s
Bio233 Genetics courseSpring, 2003
