Genotypes and Phenotypes

Question 1

what is a Genotype:

Answer 1

our genetic makeup

Question 2

what is a Phenotype?

Answer 2

observable character traits of an individual resulting from the interaction of its genotype and the environment

Question 3

How many chromosomes ?

Answer 3

Humans: 46 chromosomes, 22 pairs, 1 pair of sex chromosomes

Question 4

What defines our phenotypes?

Answer 4

Complex interaction between our genes + environment that defines who we are e.g. diet, temp, humidity, 02 levels, these factors can effect gene expression which effects the genotype.

Question 5

define a gene

Answer 5

DNA section that codes for a protein or RNA

Question 6

define an Allele

Answer 6

an allele is one of two or more versions of DNA sequence (a single base or a segment of bases) at a given genomic location.

Question 7

define a Locus

Answer 7

The location of a gene on the chromosome and at each locus an individual has 2 alleles on each homologous chromosome.

Question 8

what does it mean Genetic diversity and variation

Answer 8

refers to the combined differences in the DNA of all individuals in a species.

Question 9

define Variation

Answer 9

the differences in DNA sequences between individuals within a population.

Question 10

Why Is variation important in evolution?

Answer 10

Allows for natural selection to increase or decrease the frequency of alleles in a population.

Question 11

Genetic polymorphism

Answer 11

Multiple forms of a single gene (alleles) that exists in an individual or among a group of individuals.

Question 12

what is a Polymorphism ?

Answer 12

DNA sequence variation that Is common in the population.

Question 13

how can something be classed as a polymorphism ?

Answer 13

the least common allele must have a frequency of at least 1% in the population.

-> If the frequency is lower than this it is regarded a mutation.

->The most common polymorphisms are single base-pair differences (SNPs), small-scale insertions/deletions, STRP, microsatellite variation.

Question 14

Example of a polymorphism

Answer 14

Asian Flush:

Aldehyde dehydrogenase polymorphism (ALDH) -> (ALDH2) is a mitochondrial enzyme, abundant in the liver, that is most efficient enzyme to remove toxic acetaldehyde.

-> variant ALDH2*2: single point mutation (g->a) on exon 12 results in AA substitution from glutamine to lysine rendering the enzyme catalytically inactive.

Question 15

variant ALDH2*2 is what type of mutation, on what exon, and what is the substitution?

Answer 15

-> variant ALDH2*2: single point mutation (g->a) on exon 12 results in AA substitution from glutamine to lysine rendering the enzyme catalytically inactive.

Question 16

2 Sources of Genetic Variation?

Answer 16

Mutation and Recombination during meiosis.

Question 17

Recombination during meiosis as a source of genetic variation

Answer 17

independent assortment of chromones and genetic crossing over between chromatids of homologous chromosomes during meiosis.

Question 18

mutation as a source of genetic variation

Answer 18

alternation to the DNA sequence, mutations create new alleles in a population.

Question 19

Importance of meiosis:

Answer 19

Random alignment and crossover results in 2 gametes never having the exact combination of chromosomes.

Each has thousands of different genes

Everyone is genetically unique.

Question 20

LAW OF SEGREGATION

Answer 20

During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene

Question 21

LAW OF INDEPENDENT ASSORTMENT

Answer 21

Genes for different traits can segregate independently during the formation of gametes

Question 22

LAW OF DOMINANCE

Answer 22

Some alleles are dominant while other are recessive; an organism with at least one dominant allele will display the effect of the dominant allele

Question 23

Dominant meaning

Answer 23

only 1 allele of a gene necessary to express the trait

Question 24

Recessive meaning

Answer 24

both alleles of a gene must be identical to express the trait

Question 25

Heterozygous meaning

Answer 25

alleles of a particular gene are non-identical

Question 26

Homozygous

Answer 26

alleles of a particular gene are identical

Question 27

A Mendelian trait

Answer 27

A Mendelian trait is one that is controlled by a single gene that has two alleles in an inheritance pattern.

Question 28

Autosomal dominant inheritance who is affected?

Answer 28

Heterozygotes affected

Question 29

Autosomal dominant inheritance how are the sexes affected?

Answer 29

Males and females equally affected

Question 30

Autosomal dominant inheritance - is the disease found in the homozygous state?

Answer 30

Disease rarely found in homozygous state

Question 31

Autosomal dominant inheritance - what is the chance of an affected individual having an affected offspring?

Answer 31

every affected individual has 50% chance of having affected offspring

Every affected individual will have (at least) one affected parent

Question 32

Autosomal dominant inheritance - can the disease skip a generation?

Answer 32

Disease cannot skip a generation, i.e. there are affected individual(s) in every generation

Question 33

Examples: Autosomal dominant inheritance

Answer 33

Examples: Huntington’s disease, hypertrophic cardiomyopathy (HCM), Marfan’s syndrome (MFS), hereditary long QT syndrome (LQTS)

Question 34

Autosomal recessive inheritance - are Heterozygotes affected?

Answer 34

Heterozygotes unaffected

Question 35

Autosomal recessive inheritance - How are sexes affected?

Answer 35

Males and females equally affected

Question 36

Autosomal recessive inheritance - % of offspring having a affected offspring

Answer 36

Two heterozygotes have 25% chance of having affected offspring

Two affected (homozygous) individuals will have affected offspring only

Question 37

Autosomal recessive inheritance - can the disease skip generations ?

Answer 37

yes

Question 38

Autosomal recessive inheritance - examples?

Answer 38

Examples: sickle cell anaemia, Tay-Sachs disease

Question 39

X-linked dominant inheritance (rare) - is the disease passed from father to son?

Answer 39

The disease is never passed from father to son - the trait follows the inheritance of the X - chromosome.

Question 40

X-linked dominant inheritance - how are the daughters of an affected male impacted?

Answer 40

All daughters of an affected male and a normal female are affected (1 + 2 or 14 + 15)

Question 41

X-linked dominant inheritance - What happens if an affected daughter reproduces?

Answer 41

Affected females and normal males produce

1⁄2 of the sons affected

and 1⁄2 of the daughters affected

Males are usually more severely affected than females

Question 42

X-linked dominant inheritance

Answer 42

example: Rett syndrome…

Rett syndrome is a rare genetic neurological and developmental disorder that affects the way the brain develops. This disorder causes a progressive loss of motor skills and language. Rett syndrome primarily affects females. Most babies with Rett syndrome seem to develop as expected for the first six months of life.

Question 43

X-linked recessive inheritance - what sex is likely affected and how is the disease passed down?

Answer 43

The disease is never passed from father to son - All affected males in a family are related through their mothers

In the general population males are more likely to be affected than females

Question 44

Non-Mendelian Inheritance Mitochondrial -what is the inheritance?

Answer 44

Unlike nuclear genes, which are inherited from both parents, mitochondrial genes are inherited only from the mother.

Question 45

Non-Mendelian Mitochondrial Inheritance - how does the mother pass on the disease?

Answer 45

The disease is passed from a mother to all of her children;

sons will not pass it on, but daughters will pass it on to all of their children.

Question 46

Non-Mendelian Mitochondrial Inheritance Examples:

Answer 46

Examples: mitochondrial myopathy, diabetes mellitus and deafness (DAD), Leber’s hereditary optic neuropathy (LHON), Leigh syndrome, Myo neurogenic gastrointestinal encephalopathy (MNGIE).

Question 47

Dominance

Answer 47

the dominant allele in a heterozygote determines the phenotype

Question 48

Recessiveness

Answer 48

the non-dominant allele in a heterozygote is called recessive and its effect is masked

Question 49

Codominance

Answer 49

neither allele is dominant nor recessive and the phenotypes of both alleles are expressed

Question 50

Incomplete dominance

Answer 50

Neither allele is completely dominant nor completely recessive

Question 51

Complementation

Answer 51

Complementation occurs when two strains of an organism with different homozygous recessive mutations that produce the same mutant phenotype (for example, a change in wing structure or white eye colour in flies) have offspring that express the wild-type phenotype when mated or crossed

Question 52

Complementation test

Answer 52

A complementation test (sometimes called a “cis-trans” test) can be used to test whether the mutations in two strains are in different genes (complementation ordinarily will occur more weakly or not at all if the mutations are in the same gene)

Question 53

Example of complementation

Answer 53

Albinism - Albinism is an autosomal recessive disorder.

Two genes involved: A1 (alleles A1 and a1) and A2 (alleles A2 and a2

Question 54

Genetic linkage

Answer 54

Linked genes are genes that are likely to be inherited together because they are physically close to one another on the same chromosome.

Question 55

Recombination frequency

Answer 55

is a measure of genetic linkage and is used in the creation of a genetic or linkage map.

Question 56

Example of Genetic Linkage

Answer 56

Genes for hair and eye colour are linked, so certain hair and eye colours tend to be inherited together, such as blonde hair with blue eyes and brown hair with brown eyes.