Examples of Inbreeding and Outbreeding (2)

Question 1

What is human inbreeding?

Answer 1

Inbreeding in humans is the mating of close relatives such as mother to son, father to daughter, brother to sister, first cousin to first cousin, and is sometimes referred to as incest. There are taboos against incest in many societies and in most countries it is against the law.

Question 2

Why is human inbreeding so frowned on?

Answer 2

Human inbreeding can easily result in the offspring having a recessive genetic disease, e.g. Tay-Sachs and haemophilia.

Question 3

Why can human inbreeding have such horrendous effects? (3)

Answer 3

• Close relatives are much more likely to carry the same mutation for a recessive genetic disease. They would thus be ‘genetic carriers’ of the disease or physical abnormality.
• Thus, if the parents are related it increases the chances of the offspring receiving a harmful recessive allele from each parent.
• If this happened the offspring would be homozygous for the harmful recessive alleles, which would be expressed in the offspring who would suffer from the genetic disease.

Question 4

What are the risks of being homozygous for a genetic abnormality? The risk of a genetic disease resulting from mating with: (3)

Answer 4

• a common ancestor is about 1 in 20
• first cousins is about 1 in 11
• first degree relatives is 1 in 2

Question 5

Therefore, it can be seen that the closer the relationship the greater the risk of harmful _____ alleles being homozygous in the offspring and thus being expressed.

Answer 5

recessive

Question 6

Inbreeding was very common among the royal families of Europe, and it is likely to have been the cause of the widespread number of cases of _____ in the royal families in the 1900s.

Answer 6

haemophilia

Question 7

The presence of haemophilia in the royalty of Europe started with Queen Victoria of England. It seems that a haemophiliac gene arose by ____ in one of the gametes of her parents. Of her nine children one, a son, was a haemophiliac and two daughters were genetic carriers. The haemophiliac gene is recessive and ___-____. Being sex-linked means only the sons would suffer from the disease.

Answer 7

mutation

X-linked

Question 8

What was inbreeding seen as in the royal family?

Answer 8

Inbreeding in the royal family was seen as a major reason for the harmful recessive allele’s high incidence rate in the British royal house. Haemophilia spread rapidly with over twenty members inheriting the disease in just over 100 years. This recessive gene has since been lost in this lineage.

Question 9

What is haemophilia?

Answer 9

The blood clots much more slowly than normal, resulting in extensive bleeding from even minor injuries

Question 10

Another example of a genetic disease being caused by inbreeding is the increased prevalence of ___ ____ disease in certain Jewish populations where arranged marriages are encouraged. It is an inherited metabolic abnormality that is fatal in early childhood.

Answer 10

Tay Sachs

Question 11

Most plants naturally ____-_____ and are therefore natural outbreeders.

Answer 11

cross-pollinate

Question 12

What does outbreeding result in?

Answer 12

Outbreeding results in a high level of heterozygosity within a population which increases the genetic diversity of the plant species.

Question 13

A good example of plant outbreeding has occurred in the ____ family. As a result of the outbreeding and the resultant increased heterozygosity of wild mustard plant species some offspring showed different traits such as large ___ or large ____ or compacted flower ____.

Answer 13

Brassica
stems
leaves
buds

Question 14

Breeding with plants with these different traits led to the development of a variety of different vegetables such as ____ (large stem), kale (large leaves) and ____ (compacted flower buds) that each have a modified trait. So although they appear ___, these vegetables are the result of the outbreeding of a few species of wild Brassicas, i.e. the wild mustard plants.

Answer 14

kohlrabi
broccoli
diverse

Question 15

What is the founder effect?

Answer 15

The founder effect refers to the loss of genetic variation when a very small number of individuals from a larger population establish a new colony. This is usuallydue to migration or geographic isolation

Question 16

What happens if a new population has only a few individuals?

Answer 16

If the new population has only a few individuals, its gene pool may be quite different from that of the original population. As a result over time they will establish a new population. The new population will be different, both genetically and phenotypically to the parent population. Eventually the founder population can become a new species, related to the original but unable to interbreed

Question 17

What has led to scientists considering the founder effect important?

Answer 17

This potential for relatively rapid changes in a colony’s gene frequency has led most scientists to consider the founder effect an important driving force in the evolution of new species

Question 18

A common example of the founder effect in South Africa is the ____ (Acinonyx venator).

Answer 18

cheetah

Question 19

Until recently, it was thought that reason for the decrease in the cheetah population was due to over-hunting and habitat destruction. What is the truth?

Answer 19

However, recent genetic analysis, e.g. with mtDNA, shows that the cheetah population has an extremely low genetic diversity (90 to 99% less genetic variation than in other out-bred cat species).

Question 20

What did low genetic diversity result in?

Answer 20

This results in poor sperm quality, low fecundity, high cub mortality and sensitivity to disease. All these factors have made breeding and survivorship difficult for cheetahs – only about 5% of cheetahs survive to adulthood.

Question 21

What is fecundity?

Answer 21

the ability to produce abundant healthy offspring

Question 22

It is hypothesised that about 10 000 years ago due to ____ ____ a major extinction of large vertebrates occurred. All but a small group (the founder population) of cheetahs died out forcing close family relatives to mate with each other, or inbreed. This caused their ____ ___ diversity, much lower than the original population. This can make the population very vulnerable to extinction.

Answer 22

climatic change

low genetic