Lecture 8 - Bio 160

•After determining the genotype and phenotypes of the offspring from the Punnet square analysis, a tally is performed. For the example of freckles, what are the ratios of the previous punnet square...

-The genotypic ratio is: 1 FF: 2Ff: 1ff or 1:2:1 -The phenotypic ratio is: 3 freckles: 1 without freckles or 3:1 -Three individuals have freckles because they carry at least one dominant allele

Genotype:

alleles carried by the chromosomes that are responsible for a given trait

Sex Determination

•50/50 chance of humans having a boy or a girl. •The father has XY chromosomes and can either give an X or a Y allele •The mother has XX chromosomes and can only give an X allele. •XX - Female baby •XY - Male baby

In the cross Ff X Ff, what is the chance/probability of.......?

•Chance of freckles: ¾ or 75% -(FF) + (Ff) + (fF) = 3 out of 4 total possibilities •Chance of no freckles: ¼ or 25% -(ff) = 1 out of 4 total possibilities

Incomplete Dominance occurs when the ___________ has an intermediate phenotype between the two ______________

•Incomplete Dominance -Occurs when the heterozygote has an intermediate phenotype between the two homozygotes Ex: -Curly-haired person reproduces with a straight-haired person •Their children have wavy hair -Two wavy-haired persons reproduce with an expected phenotypic ratio of: 1:2:1 •1 curly-hair: 2 wavy-hair: 1 straight-hair

•Many traits and disorders in humans, and other organisms, are _______ in origin. •Traits are controlled by a single allele pair on the _________ chromosomes (any chromosome other than X or Y.)

•Many traits and disorders in humans, and other organisms, are genetic in origin. •Traits are controlled by a single allele pair on the autosomal chromosomes - any chromosome other than (X or Y).

•Sex-linked traits differ in their patterns of expression in males and females. -Males need to have ____ recessive allele(s) to exhibit the recessive trait -Females must have ____ recessive allele(s) to exhibit the recessive trait -Color-blindness is a(n) ___-linked trait

•Sex-linked traits differ in their patterns of expression in males and females. -Males only need to have one recessive allele to exhibit the recessive trait -Females must have two recessive alleles to exhibit the recessive trait -Color-blindness is a X-linked trait

•Skin color is the result of pigmentation produced by __________ cells. •Over ____ different genes influence skin color. •We use ______ pairs of alleles as a simplified example, (Aa, Bb, and Cc). •Each _______ allele (capital letter) contributes to pigmentation. •When a very dark person reproduces with a very light person, the children have ______-_______ skin.

•Skin color is the result of pigmentation produced by melanocyte cells. •Over 100 different genes influence skin color. •We use three pairs of alleles as a simplified example, (Aa, Bb, and Cc). •Each dominant allele (capital letter) contributes to pigmentation. •When a very dark person reproduces with a very light person, the children have medium-brown skin.

Gregor Mendel

•Understanding of genetics is based on work ofGregor Mendel •Investigated inheritance at the organism level (1860s) •Concluded that plants transmit distinct factors to offspring •Now called genes, found on chromosomes

Mendel used letters to indicate each allele: -A capital letter symbolizes a ________ allele. -A lowercase letter symbolizes a _________ allele.

-A capital letter symbolizes a dominant allele. -A lowercase letter symbolizes a recessive allele. -Dominant refers to the allele that will mask the expression of the alternate (recessive) allele, when both are present in a given organism.

Pedigree: What is it and what is it used for?

-A chart of family's history with regard to a particular genetic trait -Used to determine whether inherited condition is due to autosomal dominant or autosomal recessive allele

Phenylketonuria (PKU)

-Affected individuals lack the enzyme needed for the normal metabolism of the amino acid phenylalanine -Infants will develop normally if placed on a low phenylalanine diet -Severe mental retardation will otherwise result

Homologous pairs have certain characteristics:

-Both members have same length and centromere location -Both carry similar types of genes -Alternate forms of a gene for a trait are called alleles. -Alleles are always on the same spot, or locus.

Codominance

-Occurs when alleles are equally expressed in a heterozygote Ex: blood type AB -Red blood cells have both Type A and Type B surface antigens. -We assume both alleles code for a product, and we observe the result of both products being present.

Steps used to solve a genetics cross

1.Determine the genotype of each parent. 2.List the possible gametes from each parent. 3.Combine all possible gametes. 4.Determine the genotypes and phenotypes of all offspring.

A homozygous man with freckles reproduces with a homozygous woman without freckles •Will their children have freckles?

Yes. only possibility is Ff

Phenotype:

•an individual's actual appearance -May include physical characteristics, microscopic or metabolic characteristics

-If the two alleles are different, the individual is said to be _________.

-If the two alleles are different (hetero), the individual is said to be heterozygous.

-If the two alleles are the same, the individual is said to be _________.

-If the two alleles are the same (homo), the individual is said to be homozygous.

Huntington disease

-Neurological disorder that leads to progressive degeneration of brain cells -Caused by a mutated copy of the gene for a protein called huntingtin -Most patients appear normal until they are of middle age and have already had children -Test now exists to detect presence of gene

Solving a cross when two individuals are both Ff

-Perform a monohybrid cross -A Punnet square is useful in solving this problem

Polygenic inheritance occurs when

-a trait is governed by two or more genes (sets of alleles).

Which parents below would have the possibility of producing a daughter who is colorblind? 1.XRY x XRXR 2.XrY x XRXR 3.XRY x XrXR 4.XrY x XrXR

4.XrY x XrXR

Polygenic inheritance: Dominant alleles have a quantitative effect on the ____________, and these effects are _________. -The result is a __________ _________ of phenotypes. -An example of this is skin color.

Dominant alleles have a quantitative effect on the phenotype, and these effects are additive. -The result is a continuous variation of phenotypes. -An example of this is skin color.

Presence of freckles: -The dominant allele of freckles is assigned (F). -The recessive allele of no freckles is assigned (f). -In the case of a single trait, there are three possible combinations of the two alleles. •__, __, __

FF, Ff, ff

IA = __ antigens on red blood cells IB = __ antigens on red blood cells i = neither A nor B antigens on red blood cells Both IA and IB are dominant over i, IA and IB are _____________.

IA = A antigens on red blood cells IB = B antigens on red blood cells i = neither A nor B antigens on red blood cells -Both IA and IB are dominant over i, IA and IB are codominant

In diploid organisms, a pair of homologous chromosomes contains ____ allele(s) for each trait. -____ allele(s) on each member of the homologous pair.

In diploid organisms, a pair of homologous chromosomes contains two alleles for each trait. -One allele is on each member of the homologous pair.

In peas and humans, chromosomes come in pairs called __________ chromosomes. One member of the _____ is inherited from the ______, and the other is inherited from the _______.

In peas and humans, chromosomes come in pairs called homologous chromosomes. One member of the pair is inherited from the mother, and the other is inherited from the father.

Autosomal Recessive Pedigree A child is affected, but neither parent is. •This can happen only if the disorder is _________ and the parents are ______________. This means the parents are _______ because they are unaffected but are capable of having a child with the genetic disorder

•In this pattern, the child is affected, but neither parent is. •This can happen only if the disorder is recessive and the parents are heterozygotes. •Notice that the parents are carriers because they are unaffected but are capable of having a child with the genetic disorder.

Autosomal Dominant Disorders A child is unaffected, but the parents are both affected. •This is possible if the condition is autosomal __________ and the parents are __________. •This also illustrates that when both parents are unaffected, all their children are _________. Neither parent has a ________ gene that passes the condition on

•The child is unaffected, but the parents are both affected. •This is possible if the condition is autosomal dominant and the parents are heterozygotes. •This also illustrates that when both parents are unaffected, all their children are unaffected. -Neither parent has a dominant gene that passes the condition on.

•When two individuals with the genotype _________ reproduce with one another, their offspring may range in skin color from very dark to very light. •The phenotype distribution follows a _____-_________ curve (characteristic of a polygenic trait). -Implies that few individuals have the _________ phenotypes -Most have the phenotype that lies in the _________

•When two individuals with the genotype AaBbCc reproduce with one another, their offspring may range in skin color from very dark to very light. •The phenotype distribution follows a bell-shaped curve (characteristic of a polygenic trait). -Implies that few individuals have the extreme phenotypes -Most have the phenotype that lies in the middle