Biology 181 Chapters 14 And 15 Study Questions

Front 1

What is a genotype?

Back 1

Refers to the genetic makeup (alleles) of an individual

Front 2

What are genotype and phenotype ratios for various crosses?

Back 2

TT - Homozygous

Tt - Heterozygous

tt - Homozygous recessive

Front 3

What is a phenotype?

Back 3

Refers to the physical appearance of the individual

Front 4

What is dominance?

Back 4

Trait is visible and masks the recessive trait capital letter.

Front 5

What does it mean to be recessive?

Back 5

Trait is NOT visible (hidden), lower case letter.

Front 6

What is incomplete dominance?

Back 6

Phenotype of offspring = blend of 2 parental phenotypes

Red & white --> pink petals

Curly & straight hair --> wavy hair

Pitch of male voice
Lowest = PP
Baritone = Pp
Highest = pp

Incomplete dominance = when an intermediate phenotype is expressed
Flower color in the carnation
Sickle cell

Front 7

What is codominance?

Back 7

Codominance = alleles are equally expressed

Codominance = More than 1 allele is fully expressed
ABO blood type = multiple allelic traits

Front 8

What is a multiple allele system?

Back 8

Multiple Allelic Trait = controlled by multiple alleles (several forms)

ABO blood type = multiple allelic traits

Front 9

Are there always only two alleles for every trait?

Back 9

No, but any individual has at most two different alleles, most genes exist in a large number of allelic forms in the population as a whole. In some cases, the alleles have different effects on the phenotype, and their dominance interactions with each other can be described as a series.

Front 10

What is Mendels law of segregation?

Back 10

Mendel's first law, stating that the two alleles in a pair of segregate (separate) into two different gametes during gamete process.

Each individual has 2 factors (alleles) for each trait

Alleles segregate (separate) during gamete formation

Each gamete contains only 1 allele from each pair

Fertilization gives each new individual 2 factors for each trait

Reshuffling of genes leads to genetic variation

Front 11

What is mendels law of independent assortment?

Back 11

Mendell's second law, stating that each pair of alleles segregates, or assorts, independently of each other pair during gamete formation; applies when genes for two characters are located on different pairs of homologous chromosomes.

Each pair of genes separates independently of the other pairs

All possible combinations of genes can occur in the gametes

Front 12

How was Mendel lucky with the law of independent assortment?

Back 12

Mendel was lucky in choosing the characteristics he worked with, since the were not linked and found on separate chromosomes.

Genes that are found on the same chromosome will not follow the law unless it happens in meiosis - prophase I chromosomes.

Front 13

What does it mean to say genes are linked?

Back 13

X-linked (sex-linked) = genes carried on X chromosome
Y chromosome = missing these alleles
Y chromosome cannot offset the inheritance of an X-linked recessive allele

any pair of genes that tend to be transmitted together

Front 14

How do autosomal dominant disorders that are lethal to their owner persist in populations?

Back 14

Recessive genes, Imbreeding, low variations of chromosomes,
**Autosomal Dominant Disorder that affects 1:20,000 (Age 35-45)

So the reason these genes are capable of lasting is because they do not activate until after the breeding process.

Front 15

What are the ways in which recessive disorders persist in populations? Think tay sachs and sickle cell.

Back 15

These disorders are not necessarily life threatening and can then be passed recessively.

Intuitively, natural selection should eliminate these lethal genetic disorders from the population.....However, natural selection does not act on the genotype of an individual, but on the phenotype. Many of these lethal genetic disorders are the product of two "recessive alleles" that were masked in the parents with a "dominant allele."

Front 16

What is epistasis?

Back 16

A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited.

When 1 gene affects the expression of another gene
Albinism
Black coat color is dominant to brown in mice (B,b)
Another gene determines whether or not pigment is deposited in the hair C,c
Individuals with cc as their genotype will be albino regardless of the genotype at the coat color gene.

Epistasis = A gene at 1 locus interferes with the expression of a gene at a different locus (albinos)
Human skin color = polygenic inheritance

Front 17

What is polygenic inheritance?

Back 17

Human skin color = polygenic inheritance

Occurs when 1 trait is governed by 2 or more sets of alleles

Each dominant allele has a quantitative (additive) effect on phenotype

Result = continuous range of phenotypes
height
skin color (genes code for pigment)

Polygenic Disorders:
Cleft lip
Diabetes
Schizophrenia
Allergies
Cancer

Front 18

3 copies of chromosome 21
nondisjunction during egg & sperm formation

Sperm has extra chromosome 21 (23% of cases)

Translocation between chromosome 21 & 14 (5% of cases)

Gart gene causes mental retardation

Detected by: amniocentesis, chorionic-villi sampling, & karyotyping

Mothers 40+ years = at higher risk

Back 18

Trisomy - Down Syndrome

Front 19

Autosomal dominant disorder that affects 1:20,000 (age 35-45)

Causes progressive brain damage

Mutation in gene on chromosome 4
Abnormal huntington protein forms clumps in neurons

Symptoms:
severe muscle spasms
personality disorders
death within 10-15 years of onset

Back 19

Huntingtons Disease

Front 20

1:400 African Americans

RBC = sickle-shaped
Defect in hemoglobin
Clog vessels
Poor circulation & anemia
Resistance to malaria (1:10 = heterozygous)

blood disorder

Red blood cells = sickle-shaped due to defect in hemoglobin
Clog vessels
Poor circulation
Anemia
Resistance to malaria (heterozygous)

Back 20

Sickle Cell

Front 21

Short

Broad chest

Skin folds on neck

Nonfunctional ovaries

Do NOT undergo puberty

Back 21

Turner (XO)

Front 22

Affects 1:2000
Sterile

Undeveloped testes

Some breast development

Possible retardation

Barr body present

Back 22

Klinefelter (XXY)

Front 23

Autosomal recessive disorder that affects 1:3000 newborns

1:20 caucasians = carriers
Carriers = resistant to cholera

Mutation in gene on chromosome 7
Lack of water release leads to thick mucus

Thick mucus clogs lungs & pancreatic ducts

Life expectancy = 35 years

Back 23

Cystic Fibrosis

Front 24

Skeletal & connective tissue

Back 24

Marfan’s

Front 25

Extra fingers or toes

Back 25

Polydactyl

Front 26

Lysosome storage disorder
Affects 1:3,600 Jewish people (Ashkenazi)
Lack enzyme needed to digest glycosphingolipids
Symptoms:
Blindness, seizures & paralysis
Death by age 3 or 4
Carriers (Tt) = more resistant to Tuberculosis

Back 26

Tay-Sachs Disease

Front 27

How does environment influence phenotype?

Back 27

One of the examples includes:

If height were affected by balanced diet then that would indicate enviroment.

Himalayan rabbits & Siamese cats:
Enzyme coding for black fur = active at low temperatures
Black fur only occurs on extremities (ears, nose, feet, tail)

Front 28

How does environment influence phenotype contribute to the patterns of inheritance we see in natural populations?

Back 28

Himalayan rabbits & Siamese cats:
Enzyme coding for black fur = active at low temperatures
Black fur only occurs on extremities (ears, nose, feet, tail)

Front 29

What are some of the chromosomal level changes we can see?

Back 29

Deletion
End of chromosome breaks off

2 simultaneous breaks lead to loss of internal segment

Translocation
Chromosome segment moves from 1 chromosome to another (nonhomologous) chromosome

Down Syndrome: occurs between chromosome 21 & 14

Duplication
Chromosomal segment occurs more than once in the same chromosome

Caused by:
Unequal crossing over
Inversion

Inversion = when segment that has become separated is turned 180 Degrees and reinserted