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Date _________________ Per ___
Unit 4 Plants and Animals Reproduce REVIEW Answers
1. The genetic trait of an individual that is present but remains unexpressed is called __recessive____.
2. Having straight hair is a recessive trait. Describe what type of hair the parents must have in order for
their offspring to have straight hair.
Both parents must have straight hair and be homozygous recessive.
3. Gregor Mendel did crossbreeding experiments with round pea seeds (R) and wrinkled pea seeds (r). In
one such experiment, he ended up with 5,674 plants with round seeds and 2,080 plants with wrinkled
seeds. Make a Punnett square that could describe this experiment.
This is because 5,674 : 2,080 is approximately at 3:1 ratio with ¾
round seeds and ¼ wrinkled seeds which is what the Punnett Square above shows.
4. White-tailed deer usually have brown and white coats. The pigments that produce hair color are absent in an albino
white-tailed deer. Albinism appears in about 1 in 30,000 deer.
Why would two albino parent deer always produce albino offspring?
Because both are homozygous recessive and that is the only genotype they produce.
5. The Punnett square below shows a cross between two heterozygous corn plants that results in 3/4 tall and 1/4 short
plants.
?
?
?
tall
tall
?
tall
short
What is the genotype of the parents in this cross? (tall (T) is dominant short (t) is recessive.)
Tt X Tt would give 1 TT, 2 Tt, and 1 tt or 3 tall and 1 short.
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6. A trait that is always expressed when present in an individual is called what? Dominant
7. In some rabbits, black coat color (B) is dominant over brown coat color (b). Using a Punnett Square, predict the results
of the monohybrid cross BB × Bb for coat color.
B
B
B
BB
BB
b
Bb
Bb
100% or 4/4 would have black coat color.
8. In a plant species, the allele r produces purple flowers and the allele R produces red flowers. What cross is most likely
to produce an equal number of red and purple flowers?
Rr X rr would give ½ Rr and ½ rr
9. A mother with freckles passes this trait on to all of her four children. The father of the children does not have freckles.
Freckles are most likely controlled by what type of genes?
rsDominant genes
10. In pea plants, the allele for tall stems (T) is dominant to the allele for short stems (t). The Punnett Square below
shows a cross between a homozygous recessive (tt) parent and a homozygous dominant (TT) parent.
T
T
t
Tt
Tt
t
Tt
Tt
What is the expected distribution of genotypes of the offspring from these two parents?
100% Tt so the only trait possible is tall stems.
11. When sex cells combine to produce offspring each sex cell will contribute how many chromosomes?
½ of the original cell which is 23 in humans.
12. What is a mutation?
A permanent change in an organism’s DNA.
13. If the body cells of an organism have 10 chromosomes, then the sex cells produced during meiosis would have?
5 chromosomes
14. The process in which a parent cell divides twice to produce sex cells is called meiosis.
15. In a DNA molecule Thymine matches with what nitrogen base? Adenine
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16. Why would a mutation be harmful to an organism?
The mutation would DECREASE the organism’s chance of survival.
Write the definitions of the words below for #17 - 26.
17. Genotype - An organism’s genetic makeup or allele combination. What can’t be seen. (ex:Aa, AA, aa)
18. Phenotype - An organism’s physical appearance or visible traits. What can be seen. (ex: straight hair
or curly hair)
Alleles - 2 forms of a gene, 1 from each parent and represented by lower case and capital letters. (ex: AA,
Aa, aa)
20. Chromosomes – Chromosomes are made of DNA. The order of the DNA in the genes determine our
traits.
21. Genes – Genes are segments of DNA that are located in a chromosome and that codes for a specific
hereditary trait.
22. Homozygous - Also known as purebred. The allele combination is the same, both dominant (AA) or
both recessive (aa).
23. Heterozygous - Also known as a hybrid, is when the allele combination is one of each, one dominant
and one recessive. (Aa)
24. DNA - DNA is deoxyribonucleic acid and is the genetic code that determines an organism’s traits. It is
found in a cell’s nucleus.
25. Dominant Trait – a trait that is expressed or seen in an organism, always overrides a recessive trait
26. Recessive Trait – a trait that is unexpressed or hidden in our genes, only shows when paired with
another recessive allele
27. What type of cells are produced during meiosis? Gametes = Sex Cells
28. What is an advantage of sexual reproduction in the survival of a population? Genetic diversity!!! Allowing
organism’s to change or time and adapt to their surroundings or changes in their environment.
29. The process where the cell grows, functions, and divides into new cells is referred to as what? Cell Cycle
30. What is the first stage of the cell cycle where the cell grows and the DNA is copied? Interphase
31. A DNA molecule is shaped like what? A double helix or a spiral staircase
32. What is probability? Probability is the likelihood that an event will occur. What chance does it have of
happening?
33. What does a Punnett square show? Punnett squares are a useful tool for predicting what traits an
organism’s offspring will have when plants or animals breed. They show the possible genetic
crosses.
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Date _________________ Per ___
34. What determines the genetic code? Genetic code is the order of nitrogen bases (A, T, G, C) along a gene.
This order or sequence determines our traits. It is like the recipe of how we are made.
*35. Chromosomes are made up of what? Genes
36. Genetic disorders are caused by what? Mutations in DNA during interphase