Laboratory 20: the pattern of inheritance

In pea plants, tall (T) is dominant and short (t) is recessive. A heterozygous tall plant is crossed with short plant. What is the expected phenotypic ratio?

1:1

Color of corn kernels conclusion Pp x pp

20.2 Phenotypic ratio 1:1 one purple kernel to one yellow kernel • Do your results differ from the expected phenotypic ratio? Yes Explain. Counting small numbers of offspring is more likely to cause a variation from the expected ratio. • Was your class data closer to the expected phenotypic ratio than your individual data? Yes, the larger the number of offspring observed, the closer the ratio to the expected results.

If the cross in problem 6 produces 220 plants, how many offspring have green pods and how many have yellow pods?

55 have yellow pods and 165 have green pods. If the cross in #2 produces 220 plants, how many offspring are tall and how many are short? 110 are tall and 110 are short.

PpSs x PpSs expected phenotypic ratio

9:3:3:1 (9 purple smooth to 3 purple rough to 3 yellow smooth to 1 yellow rough)

One trait crosses

A single pair of alleles is involved

In horses, black (B) and trotting gait (T) are dominant, while brown (b) and a pacing gait (t) are recessive. If a black trotter (homozygous for both traits) is mated to a brown pacer, what phenotypic ratio is expected among the offspring?

All black trotter

Individuals have 2 alternate forms of genes (alleles) for each trait in their body cells

Alleles are on the chromosomes

In animals such as fruit flies, chromosomes differ between the sexes. All but one pair of chromosomes in males and females are the same, these are called

Autosome because they do not actively determine sex

What is the name given to the chromosomes that do not actively determine the gender of an organism?

Autosomes

homozygous dominant

Both alleles (factors) for a trait are the same and dominant (AA)

homozygous recessive

Both alleles (factors) for a trait are the same and recessive (aa)

If a trait is an X-linked recessive trait, why is it unlikely that many females with the recessive trait (e.g., white eyes in fruit flies) phenotype will exist?

Both of a female's X chromosomes would have to carry the X-linked recessive allele for a female to have the recessive trait phenotype. If just one of a female's X chromosomes carries the X-linked recessive allele, the other X chromosome with the dominant allele will mask the recessive one.

What is the cross between two individuals with GgRr genotypes called?

Dihybrid cross

Conclusions: Color and Texture of Corn

Do the results differ from the expected ratio per individual data? Most likely. Per class data? Closer to expected ratio Explain. The more offspring counted, the greater the probably of achieving the expected ratio.

Conclusion Wing Length and Body Color in Drosophila

Do the results differ from the expected ratio per individual data? Yes, probably Per class data? Not as much Explain. The more offspring that are counted, the greater is the probability of achieving the expected ratio.

Wing length and body color of Drosophila

Drosophila: are tiny flies you often see flying around rip fruit therefore they are called fruit flies. In Drosophila, long wings (L) are dominate over short wings (l) and grey body (G) is dominate over black body (g) Cross LiGg x llgg (phenotypic cross 1:1:1:1)

State two new crosses that could not produce fruit flies heterozygous in both traits?

GGLL x GGLL, GGLL x GgLL, or GGLl x GGLl (any combination in which the offspring must receive two capital letters for one of the traits) Also ggll x ggll in which all offspring would receive two small letters.

Whereas individuals have two alleles for every trait

Gametes have only one allele because alleles are on the chromosomes and homologues separate during meiosis

What word is used to describe the possession of one dominant allele and one recessive allele?

Heterozygous

If the phenotypic ratio among the offspring is 3:1, what is the genotype of the parents?

Heterozygous (both)

Using words, what are the likely parental genotypes if the results of a two-trait problem are 1:1:1:1 among the offspring?

Heterozygous in both traits (x) homozygous recessive in both traits

In tobacco plants, a dominate allele (C) for chlorophyll gives the plants a green color, and a recessive allele (c) for chlorophyll causes a plant to appear white

If a tobacco plant is homozygous for the recessive allele (c) it cannot manufacture chlorophyll and thus appears white

Color of corn kernels

In corn plants, the allele for purple kernel (P) is dominate over the allele for yellow kernel (p)

The pair that is different is called the SEX CHROMOSOMES

In fruit flies and humans the sex chromosomes in females are XX and those in males are XY

Which of Mendel's laws says the separation of one pair of alleles into gametes does not impact the separation of a second pair of alleles into gametes?

Independent assortment

Phenotype

Individual appearance

Genotype

Individual genes

Males with a normal chromosome inheritance are never heterozygous for X-linked alleles and if they

Inherit a recessive X linked allele it will be expressed

Dihybrid cross

Involves two pairs of alleles, when two dihybrid individuals (AaBb) reproduce, the phenotype ratio among the offspring is 9:3:3:1, representing 4 possible phenotypes. These results can only be obtained if the alleles of the parents segregate independently of one another when the gametes were formed.

law of independent assortment

Members of an allelic pair segregate (assort) independently of the members of another allelic pair. Therefore all possible combinations of alleles can occur in the gametes.

Law of Segregation

Mendel's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete Each organism contains two alleles for each trait, and the alleles segregate during the formation of gametes. Each gamete egg or sperm then contains only one allele for each trait. When fertilization occurs the new organism have two alleles for each trait one from each parent

Can a female fruit fly that is homozygous dominant for red eyes have any offspring (male or female) with white eyes?

No

How many of the offspring of the cross between two GgRr individuals will show the recessive phenotype for both traits?

One

In pea plants, green pods (G) is dominant and yellow pods (g) is recessive. When two pea plants with green pods are crossed, 25% of the offspring have yellow pods. What is the genotype of all plants involved?

Parents are Gg 75% of offspring are Gg 25% of offspring are gg

Unexpectedly to the farmer, two tall plants have some short offspring. What is the genotype of the parent plants and the short offspring?

Parents are Tt and offspring is tt.

Chimpanzees are not deaf if they inherit both an allele E and an allele G. A cross between two deaf chimpanzees produces only chimpanzees that can hear. What are the genotypes of all chimpanzees involved?

Parents eeGG x EEgg Offspring EeGg

What word is used to refer to an individual's appearance?

Phenotype

What is used to determine the results of a cross between individuals with known genotypes?

Punnet square

monohybrid cross

Reproduction between two heterozygous individuals (Aa) resulting in a both dominate and recessive phenotype among the offspring

Which of Mendel's laws says alleles separate during gamete formation so that each gamete contains only one allele for each trait.

Segregation

Color of tobacco seedlings conclusion Cc x Cc

Table 20.1 Phenotypic ratio is 3:1 three green plants to one white Mandela's found that the more plants he counted, the closer he came to the expected ratio because the more crosses you observe the more likely it is that all type of sperm and eggs will have a chance to come together Do your results differ from the expected phenotypic ratio? Yes Explain. Counting small numbers of offspring is more likely to cause a variation from the expected ratio.

Some alleles on the X chromosome have nothing to do with gender, and these genes are said to be X-LINKED

The Y chromosome does not carry these genes and indeed carries very few genes

In corn plants, the alleles for purple kernel (P) is dominate over the allele for yellow kernel (p) and... (Pp)

The allele for smooth kernel (S) is dominate over the Allele for rough kernel (Ss)

​A breeder wants to know if a dog is homozygous black or heterozygous black. If the dog is heterozygous, which cross is more likely to produce a brown dog, Bb x bb or Bb x Bb? Explain.

The cross Bb x bb gives a 50% chance of a brown dog but Bb x Bb gives a 25% chance of a brown dog.

Homozygous dominate and heterozygous individuals show

The dominate phenotype

Homozygous recessive individuals show

The recessive phenotype

If an organism displays the dominant trait phenotype (e.g., green color in tobacco plants), it is uncertain whether the organism's genotype is homozygous dominant (CC) or heterozygous (Cc). What kind of cross (a known genotype) could be done to determine the genotype of the unknown organism? Explain your reply by describing the expected offsprings' phenotypes.

The unknown organism could be crossed with an organism with the recessive trait phenotype (e.g., white color in tobacco plants) since it has a known genotype (cc). All the offspring will have the dominant trait phenotype if the unknown organism is homozygous dominant (CC). If the unknown organism is heterozygous (Cc), then there will be offspring with the recessive trait phenotype.

If you count 52 purple rough corn kernels and 50 yellow smooth corn kernels, how many purple smooth corn kernels should you expect to count? How many yellow rough corn kernels should you expect to count? Explain your reply.

There should be about 153 purple smooth corn kernels and about 17 yellow rough corn kernels. The ratio of phenotypes is 9:3:3:1 when a dihybrid cross is done.

The chance of an equal number of gametes with A and a improves as number of the gametes increases

Therefore the 3:1 ratio among offspring is more likely the more offspring you count for the same type of cross

How many different kinds of gametes can be produced by a parent with a Ggrr genotype?

Two

In tomatoes, tall is dominant and short is recessive. Red fruit is dominant and yellow fruit is recessive. Choose a key for height T= tall, t= short for color of fruit R = red, r = yellow

What is the genotype of a plant heterozygous for both traits? TtRr What are the possible gametes for this plant? TR, tR, tr, Tr

In pea plants purple flowers (P) is dominant and white flowers (p) is recessive.

What is the genotype of pure-breeding white plants? Pure-breeding means that they produce plants with only one phenotype, pp If pure-breeding purple plants are crossed with these white plants, what phenotype is expected? Purple plants

A brown dog is crossed with two different black dogs. The first cross produces only black dogs and the second cross produces equal numbers of black and brown dogs.

What is the genotype of the brown dog? bb The first black dog? BB The second black dog? Bb

How would a tobacco seeding with the genotype cc for chlorophyll be described?

White

What are the alternate forms of a gene called?

alleles

Two black trotters have a brown pacer offspring. What is the genotype of all horses involved?

black trotter parents (BbTt) brown pacer offspring (bbtt)

Which matings could produce fruit flies heterozygous in both traits? Write yes or no beside each. (You do not need a key.)

ggLl x Ggll Yes GGLl x ggLl Yes GGLL x ggll Yes Explain. In each cross, it is possible to choose a GgLl combination for the offspring.

​In horses, two trotters are mated to each other and produce only trotters; two pacers are mated to each other and produce only pacers. When one of these trotters is mated to one of the pacers, all the horses are trotters. Create a key and show the cross.

key T = trotter, t = pacer; cross TT x tt

Heterozygous

one dominant and one recessive allele Gg

The phenotypic ratio among the offspring for two corn plants producing purple and smooth kernels is 9:3:3:1. (See lab for the key.) What is the genotype of these plants?

parental plants (PpSs) the 9 offspring- purple smooth 3 of the offspring- purple rough the other 3- yellow smooth the 1 offspring- yellow rough

If the allele for a purple corn kernel (P) is dominant over the allele for a yellow corn kernel (p), what is the genotype of the yellow kernel?

pp