D3.2 Inheritence

What is a gene and why is the study of genes important?

a region of DNA that codes for a particular characteristic.

It is important to study genes so that you can see which specific diseases may run in your family.

what is an allele?

Different varieties of the same gene located at the same position

what is a locus?

the location of a gene on a chromosome

what does co dominant mean?

Both alleles have an effect on the phenotype

what does genotype mean?

The combination of alleles inherited by an organism

what does phenotype mean?

The observable traits of an organism resulting from genotype and environmental factors

what do diploid individuals have?

two copies of each chromosome, one from their male parent, one from their female parent

what is the theory of blending inheritence?

the theory that offspring have a blend of their parents’ characteristics.

how are alleles inherited?

An individual inherits two alleles, one from each parent.

what can happen as a result of a mutation?

The base sequences of the two alleles can be slightly different from each other

what 2 things can this mutation cause?

1) can cause variations in the protein that’s produced

2) they can change protein expression proteins that affect traits so different phenotypes may be produced.

what is phenotypic plasticity?

where 1 genotype to produce different phenotypes in response to environmental conditions.

what type of adaptation is phenotypic plasticity? and why

reversible adaptation because it involves switching a gene on and off and the genes do not get turned into alleles.

what is PKU caused by?

by mutations in the gene that helps make an enzyme called phenylalanine hydroxylase.

what is phenylalanine hydroxylase needed for?

to convert the amino acid phenylalanine into tyrosine

what happens when a mutation occurs in the PAH gene?

the body cannot break down phenylalanine which can cause harm when it builds up in a person’s body.

what cells are sensitive to phenylalanine?

nerve cells.

what is sickle cell anemia?

it is a genetic blood disorder caused by a single nucleotide polymorphism in the gene for the beta-globin protein.

what base substitution causes sickle cell?

guanine base is replaced by a thymine base.

What amino acid change occurs as a result of sickle cell?

glutamic acid changes to valine.

What is polymorphism?

the possibility of two or more traits being expressed for one gene.

what is a single nucleotide polymorphism?

a variant at a single base position in the DNA.

what is an example of multiple alleles?

ABO blood groups.

what are the 3 alleles present in human blood groups?

IA,IB,i

what do the 3 alleles produce?

a glycoprotein in the red blood cells.

what does IA do?

it adds acetyl galactosamine to the glycoprotein sequence to make antigen A.

what does IB do?

it adds galactose the glycoprotein sequence to make antigen B.

what does IA IB do?

it adds both acetyl galactosamine and galactose to make both antigen A and B.

what does i do?

it is recessive so it doesn’t cause any change in the glycoprotein.

what is an example of co dominance?

the AB blood group IA IB adds both acetyl galactosamine and galactose to make both antigen A and B and both are expressed equally.

what must the doctors consider before a blood transfusion? and how

they must consider the patients ABO blood group and Rh factor by using commercially prepared antibodies.

how do doctors determine a patients blood type?

they mix the patients blood with Anti-A,B and D antibodies and if agglutination (clumping) occurs it means the antigen is present.

what is incomplete dominance?

a genetic cross in which two codominant alleles produces a distinct heterozygote blend which forms an intermediate phenotype.o

what is gene linkage?

it is where the alleles are close together on the same chromosome to be transmitted together as an intact unit through meiosis.

are genes on separate chromosomes linked?

no

what genes are more likely to be separated during crossing over?

Genes that are farther away from each other

how are recombinants formed?

by meiosis because bivalents form and crossing over can happen.

what is sex linkage?

where genes that are located on the sex chromosomes have expression and inheritance patterns that differ between males and females.

what is an example of a sex-linked genetic disorder?

Haemophilia

what is haemophilia?

a condition that occurs when there is a mutation in the clot factor gene, it affects males due to them only having one X-chromosome.

who is usually the carrier of haemophilia and why?

Females because they have XX chromosomes.

what is variation?

the differences that exist between individual organisms.

what is polygenic inheritance?

the inheritance of traits that are determined by more than one gene.

what are 4 examples of polygenic inheritance?

height, eye color, skin colour and hair color