Biology Chapter 3.4

Front 1

Mendel discovered the principles of inheritance with experiments in which ----

Back 1

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

Front 2

Gametes are ----so contain only --- allele of each gene

Back 2

Gametes are haploid so contain only one allele of each gene

Front 3

The two alleles of each gene separate --- haploid daughter nuclei during meiosis.

Back 3

The two alleles of each gene separate into different haploid daughter nuclei during meiosis.

Front 4

Fusion of gametes results in -- zygotes with two alleles of each gene that may be the same allele or different alleles

Back 4

Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles

Front 5

--alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.

Back 5

Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.

Front 6

Many genetic diseases in humans are due to --- alleles of autosomal genes although some genetic diseases are due to - or --alleles.

Back 6

Many genetic diseases in humans are due to recessive alleles of autosomal genes although some genetic diseases are due to dominant or co-dominant alleles.

Front 7

Some genetic diseases are -- linked. The pattern of -- is different with sex-linked genes due to their -- on --- chromosomes

Back 7

Some genetic diseases are sex linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes

Front 8

Many genetic diseases have been identified in humans but most are very ---.

Back 8

Many genetic diseases have been identified in humans but most are very rare.

Front 9

--and --- chemicals increase the mutation rate and can cause genetic diseases and cancer.

Back 9

Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.

Front 10

Who was Gregor Mendel?

Back 10

- published about his experiments with garden pea plants

- Gregor Mendel used artificial pollination in a series of experiments in which he carefully chose the pollen of various plants to fertilize other individuals of the same species.

Front 11

What is a Genotype?

Back 11

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

Front 12

What is a Phenotype?

Back 12

The characteristics or traits of an organism. Examples: fi ve fi ngers on each hand, colour blindness, type O blood. Dominant allele – An allele that has the same effect on the phenotype whether

Front 13

What are dominant alleles?

Back 13

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. Example: 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.

Front 14

What are recessive alleles?

Back 14

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

Front 15

What are co-dominant alleles?

Back 15

Pairs of alleles that both affect the phenotype when present in a heterozygote. Example: a parent with curly hair and a parent with straight hair can have children with different degrees of hair curliness, because both alleles infl uence hair condition when both are present in the genotype.

Front 16

What is a locus?

Back 16

The particular position on homologous chromosomes of a gene (as seen in Figure 3.2 and labelled in Figure 3.21). Each gene is found at a specifi c place on a specifi c pair of chromosomes.

Front 17

How is Homozygous?

Back 17

Having two identical alleles of a gene (see Figure 3.21). Example: AA is a genotype that is homozygous dominant, whereas aa is the genotype of someone who is homozygous recessive for that trait.

Front 18

What is heterozygous?

Back 18

Having two different alleles of a gene (see Figure 3.22). This results from the fact that the paternal allele is different from the maternal one. Example: Aa is a heterozygous genotype

Front 19

What is a carrier?

Back 19

An individual who has a recessive allele of a gene that does not have an effect on the phenotype. Example: Aa carries the gene for albinism (like the penguin in the photo on the next page) 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 progeny could be affected (because they would be aa).

Front 20

What is a test cross?

Back 20

Testing a suspected heterozygote plant or animal by crossing it with a 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.

Front 21

What is albinism?

Back 21

Most animals are unaffected by albinism and have pigmented skin, hair, eyes, fur, or feathers. But some animals lack pigmentation. An individual with little or no pigmentation is called an albino.

Front 22

When forming a punnett grid for humans, how should we interpret the data?

Back 22

there is a 50% chance of producing offspring with genotype Aa and a 50% chance of producing offspring with genotype aa. Because humans tend to produce a small number of offspring, this is the interpretation that should be used. If the example was about plants that produce hundreds of seeds, the results could be interpreted in the following way: 50% of the offspring should be Aa and the 50% should be aa.

Front 23

Each offspring is the result of ____coming together when the gametes fus.

Back 23

each offspring is the result of two alleles coming together when the gametes fuse. In this process, the two haploid sex cells join to make a single diploid cell called a zygote. This is the fi rst cell of the new offspring.

Front 24

What can the phenotypes be deduced from?

Back 24

the phenotypes can be deduced by looking at the genotypes

Front 25

Diseases such as cancer can sometimes be caused by ___chemmicals

Back 25

mutagenic

Front 26

What happens with radiation?

Back 26

When radiation hits a DNA molecule, it can sometimes knock one or more base pairs out of place, modifying the genetic code. This causes a mutation that, as we have seen, can sometimes be benign (not harmful), but at other times it can be harmful to an organism. When the DNA mutation leads to cancer, as happened to Marie Curie, the organism’s health is in jeopardy.

Front 27

What are sources of radiation?

Back 27

Nuclear bombs and nuclear power plants

Front 28

Explain why more men are affected by colour blindness than women?

Back 28

Because the allele for colour blindness is recessive and sex linked, in order for a woman to be colour blind, she must have two recessive alleles, one on each of her X chromosomes: XbXb. In any other case, she would be carrying at least one dominant allele to cancel out the effects of the colour blindness allele. In most populations, it is rare to receive one of these recessive alleles and even more rare to get both alleles for colour blindness. On the other hand, it is much easier for a man to get the condition because there is no locus on the Y chromosome to carry a dominant allele to mask the recessive allele on his X chromosome. As a result, the presence of just one b allele is enough to give him colour blindness.

Front 29

Using the CR and CW alleles for co-dominance in snapdragon flower colour, show how two plants could have some white-flowered offspring, some pink-flowered offspring and some red-flowered offspring within one generation.

Back 29

The answer should show the Punnett grid for the cross CRCW × CRCW.

Front 30

Draw a pedigree chart of the two generations described in question 12.

Back 30

In the top row, one circle and one square should be joined by a horizontal line. They should both be labelled pink. In the next row, showing the F1 generation, the four offspring plants should show one red, two pink and one white.

The offspring are shown here as all female, but any combination of shapes could be used.

Front 31

Look at the grid below showing the chances that a couple’s children might have haemophilia. (a) State the genotype of the mother and father. (b) State the possible genotypes of the girls and boys. (c) State the phenotypes of the girls and boys. (d) Who are the carriers in this family? (e) What are the chances that the parents’ next child will be a haemophiliac?

Back 31

(a) XHXh for the mother and XHY for the father. (b) Girls can be either XHXH or XHXh and the boys can be either XHY or XhY.

(c) Both possible genotypes for the girls give them normal blood clotting. The genotype XHY gives a boy with normal blood clotting but XhY is a boy with haemophilia.

(d) The only carriers are the mother and any daughters with XHXh. (Males cannot be carriers.)

(e) 1 in 4, or 25%