Chapter 3.4 Inheritance

Question 1

Mendel

Answer 1

discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed

Question 2

Genotype

Answer 2

the symbolic representation of the pair of alleles possessed by an organism, typically represented by two letters ex: Bb, GG, tt

Question 3

Phenotype

Answer 3

the characteristics or traits of an organism. ex: 5 fingers on each hand, colour blindness, type O blood.

Question 4

Dominant allele

Answer 4

An allele that has the same effect on the phenotype whether it is paired with the same allele or a different one. Dominant alleles are always expressed in the phenotype
ex: the genotype Aa gives the dominant A trait because the a allele is masked, the a allele is not transcribed or translated during protein synthesis

Question 5

Recessive allele

Answer 5

an allele that has an effect on the phenotype only when present in the homozygous state. ex: aa gives rise to the recessive trait because no dominant allele is there to mask it.

Question 6

Co-dominant alleles

Answer 6

pairs of alleles that both affect the phenotype when present in a heterozygote. ex: a parent with curly hair and a parent with strait can have children with different degrees of hair curliness, because both alleles influence hair condition when both are present in the genotype.

Question 7

Locus

Answer 7

the particular position on homologous chromosomes of a gene. Each gene is found at a specific place on a specific pair of chromosomes

Question 8

Homozygous

Answer 8

having two identical alleles of a gene. ex: AA is a genotype that is homozygous dominant, whereas aa is the genotype of someone who is homozygous recessive for that trait.

Question 9

Heterozygous

Answer 9

Having two different alleles of a gene. This results from the fact that the paternal allele is different from the maternal one. ex: Aa is a heterozygous genotype

Question 10

Carrier

Answer 10

An individual who has a recessive allele of a gene that does not have an effect on the phenotype. ex: Aa carries the gene for albinism but has pigmented skin, which means an ancestor must have been albino and some offspring might be albino; if both parents are unaffected by a recessive condition yet both are carriers, some of their offspring could be affected.

Question 11

Test cross

Answer 11

Testing a suspected heterozygote plant or animal by crossing it with known homozygous recessive (aa). Because a recessive allele can be masked, it is often impossible to tell whether an organism is AA or Aa unless they produce offspring that have the recessive trait. An example of a test cross is shown later in this section when we explore three generations of pea plants.

Question 12

Punnett grid

Answer 12

to show all the possible combinations of genetic information for a particular trait in a monohybrid cross. A monohybrid cross is one in which the parents have different alleles and which shows the results for only one trait.

Question 13

Autosomal Recessive Diseases

Answer 13

Diseases caused by recessive alleles and the locus of their gene is found on one of the first 22 pairs of chromosomes but not on the sex chromosomes X and Y. (albinism, cystic fibrosis, sickle cell disease, phenylketonuria, Tay Sachs disease, Thalassemia)

Question 14

Sex Linked genetic trait

Answer 14

genetic trait whose gene has its locus on the X or the Y chromosome. Often genetic traits that show sex linkage affect one sex more than the other: Color Blindness and Hemophilia.

Question 15

Haemophilia

Answer 15

a disorder in which blood does not clot properly.