Topic 12.2: Inheritance

Question 1

what are the different types of inheritance

Answer 1

mendelian/monogenic = one gene
mitochondrial
polygenic = many genes
complex or multifactorial = genes + environment

Question 2

what kind of environment can affect genotype and phenotype

Answer 2

radiation
chemicals
mutagens
diet
lifestyle

Question 3

what are the two ways phenotype can be affected

Answer 3

genotype and environment

Question 4

what are examples of genotype that affects phenotype

Answer 4

cystic fibrosis

Question 5

what are examples of environment that affects phenotype

Answer 5

infection

Question 6

what are examples of genotype and environmental factors that affects phenotype

Answer 6

diabetes
cancer
heart disease

Question 7

what are some features of autosomal recessive individuals

Answer 7

heterozygotes unaffected ( as for recessive needs both alleles of the gene to be present for it to have an effect in an individual), so the affected individuals must be homozygous recessive
two affected individuals will only have affected offspring
two heterozygotes (carriers) have 25% chance of having affected offspring
males and females are equally affected as its on an autosome not sex linked
disease ‘comes out of nowhere’
disease can skip generations

Question 8

what are some features of autosomal dominant individuals

Answer 8

heterozygotes affected ( as only need one allele to inherit to have an effect in an individual)
autosomal dominant diseases rarely found in homozygous state, so assume heterozygous
every affected individual (so heterozygous as that is disease) has 50% chance of having affected offspring
males and females equally affected
every affected individual will have at least one affected parent so cannot skip a generation

Question 9

what is an example of a disease that has autosomal dominant inheritence

Answer 9

huntington’s disease

Question 10

what is an example of a disease that has autosomal recessive inheritence

Answer 10

CF

Question 11

what are some features of X linked recessive individuals

Answer 11

males and females unequally affected - males more
every affected (hemizygous =genes on X chromosome) male will have at least a heterozygous carrier mother to give X chromosome to son as Y is from dad
every affected female will have an affected father and a carrier mother (one from mum, one from dad)
affected males will have at least heterozygous daughters (male gives affected X chromosome to daughters, so must have at least one allele)

Question 12

what is an example of a disease that has x linked recessive inheritence

Answer 12

haemophilia A

Question 13

what are some features of X linked dominant individuals

Answer 13

females more likely to be affected
hemizygous males and heterozygous females affected
heterozygous affected females have 50% chance of having affected offspring
affected males cannot give trait to sons as males give Y chromosome to sons but will give to all daughters and they will all be affected

Question 14

what are some features of Y linked recessive individuals

Answer 14

only males affected
affected males give traits to all their sons
diseases linked to maleness

Question 15

what are some features of mitochondrial inhertied individuals

Answer 15

all individuals will inherit from their mother (egg has lots more mitochondria than sperm, and sperm mitochondria not enter egg)
mother affected = all children affected
mither unaffected = all children unaffected

Question 16

what are some features of polygenic inherited individuals

Answer 16

more than one gene can be involved in producing a phenotype
genes on the same chromosomes are said to be linked
genes on different chromosomes are not linked
linked genes do not show independent assortment at meiosis because genes on same chromosome so alleles travel together in meiosis (so not a 1:1:1:1 ratio as more likely to not bother crossing over)
so recombination frequency (amount of crossing over) between two linked genes is dependent on distance between the genes, more DNA in between more chance of crossing over taking place as otherwise too close together = tightly linked, linked genes that are far apart on same chromosome = like unlinked genes and lots of crossing over

Question 17

what is an example of a condition involving polygenic inhertince in recessive manner

Answer 17

albinism
one of two genes involved in pathway is not working properly but both alleles of that gene affected - for both parents that have albinism, but child is heterozygous so unaffected