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Study Guide – Chapter 6
Meiosis, Mendel and Punnett Squares
6.1
Define the following.
Somatic cell – body cells, make up most of your body tissues and organs. Example: spleen,
kidneys, eyeballs
Gamete – sex cells, Example: eggs, sperm
Homologous chromosome – 2 chromosomes – one inherited from the mother, one from the
father – that have the same length and look – they have copies of the same genes although the
copies may differ
Diploid – 2n – a cell that has 2 copies of each chromosome – one from the mom and one from the
dad
Haploid – n – a cell that has only one copy of each chromosome
Meiosis – cell division that divides a diploid cell into a haploid cell – necessary for sexual
reproduction.
Fertilization – the fusion of an egg and sperm
Think about it and complete the following questions FULLY!!!
Where are the germ cells located in the human body?
In the reproductive organs – the ovaries and testes
Is the cell that results from fertilization a haploid or diploid cell? Explain why.
Diploid – the combination of 23 chromosomes from the mom and 23 chromosomes from the dad
restores the diploid number to 46.
Does mitosis or meiosis occur more frequently in your body? Explain why.
Mitosis occurs throughout an organisms lifetime throughout many cells of the entire body,
compared to meiosis, which only occurs at certain times and only in the reproductive organs.
Do you think the Y chromosome contains genes that are critical for an organism’s survival?
Explain your reasoning.
No, females do not have a Y chromosome, and they are able to survive
6.3
Define the following
Trait – distinguishing characteristics that are inherited such as eye color, tail length, leaf color
Genetics – the study of biological inheritance patterns and variation in organisms
Purebred – A uniform, genetic line (example: a line of plants that has self-pollinated for long
enough)
Cross – the mating of two organisms
Law of Segregation – states that
1. organisms inherit two copies of each gene, one from each parent
2. organisms donate only one copy of each gene in the gametes, thus the two copies
of each gene segregate, or separate during gamete formation
Answer the following questions in complete sentences.
Who is Mendel? What did he study?
Mendel was an Austrian monk in the 1800’s - laid the groundwork for genetics. He is called the
“father of genetics.” He revealed patterns of inheritance.
Why is it important that Mendel began with purebred plants?
The units of color (purple and white) were both individually present. They had neither blended
together nor vanished.
Practice
Complete the following problems.
A heterozygous, smooth pea pod plant is crossed with a wrinkled pea pod plant. Predict the
offspring from this cross.
a. What is the genotype of the parents?
Ss and ss
b. Set up a Punnett Square with possible gametes.
c. Fill in the Punnett square.
6.4
d. What is the predicted genotypic ratio for the offspring?
Ss:ss
2 :2
e. What is the predicted phenotypic ratio for the offspring?
Smooth : Wrinkled
2
:
2
Define the following
Gene – a piece of DNA that provides a set of instructions to a cell to make a certain protein.
Allele – any alternative forms of a gene that may occur at a specific locus
Homozygous – two of the same allele at a specific locus
Heterozygous – two different alleles at a specific locus (example: one codes for white flowers
while the other codes for purple flowers)
Genotype – the genetic makeup of a specific set of genes – the LETTERS
Phenotype – the physical characteristics, or traits, of an individual organism – WHAT IT LOOKS
LIKE
Dominant – the allele that is expressed when two different alleles or two dominant alleles are
present
Recessive – the allele that is only expressed when two copies are present
Answer the following questions in complete sentences.
How are the terms genes, locus and allele related?
All have something to do with a particular segment of DNA, or nucleotides. A gene is a region of
DNA, a series of nucleotides that codes for a protein. It can come in different forms, called alleles,
that code for the same general type of information but the specific vary. The locus tells where a
particular gene or allele is located on a chromosome.
Explain why an organism’s genotype may be homozygous dominant, homozygous recessive or
heterozygous, but never heterozygous recessive.
The only way a phenotype or genotype can be recessive is if both alleles are recessive.
Explain the difference between phenotype and genotype.
Phenotype is the physical characteristics – or what you see – genotype are the letters
representing the alleles.
A purebred tall plant is crossed with a purebred short plant. All the F1 offspring are tall. What
can you say about the allele for tallness?
The tallness is the dominant gene.
Practice.
In humans, widow’s peak (W) is dominant over straight hairline (w).
A heterozygous man for this trait marries a woman who is also
heterozygous.
a. What are the parents genotypes?
Ww and Ww
b. List possible genotypes of their offspring
WW and Ww and ww
c. List the phenotypic ratio for their children
Widow’s Peak : Straight hairline
3
:
1
6.5
Define the following
Punnett square – a grid system for predicting possible genotypes of offspring
Monohybrid cross – cross that examines the inheritance of only one trait
Dihybrid cross – cross that examines the inheritance of two different traits
Law of Independent Assortment – that allele pairs separate independently of each other during
gamete formation, or meiosis.
Probability – the likelihood, or the chance, that a particular event will happen.
Answer the following questions.
F = purple
f = white
From an FF x FF cross, what percent of offspring would have purple flowers?
100%
What do the grid boxes in a Punnett square represent?
The possible offspring
How did Mendel’s dihybrid crosses help him develop his second law?
Mendel was able to observe that the inheritance of one trait did not influence the inheritance of a
second trait.
A fruit fly has diploid cells with 8 chromosomes. Explain how many chromosomes are in it
haploid gametes.
4 chromosomes = half = haploid
Meiosis is a continuous process, but we can think of it as taking place in 2 stages, Meiosis I and
Meiosis II. Describe the products of each stage. How do the products of Meiosis I differ from
those of Meiosis II?
Meiosis I divides homologous chromosomes, produces diploid cells
Meiosis II divides sister chromatids., produces haploid cells
Gametes
Each of the arrows is pointing to
a different part of the Punnett
square, what do those letters
represent?
Possible offspring
REMEMBER TO GET MORE PRACTICE USING THE DIRECTIONS BELOW!!
Please go to www.classzone.com
- choose High School Science and New Jersey
- choose Biology 2010 Book
- Under “Assessment,” Select “Section Quizzes”
- Choose Unit 3: Genetics on the left hand column
- Take the quizzes for the Chapter 6.1 – Chapter 6.4