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Mendel’s Laws of Heredity
Who was Gregor Mendel?
Gregor Mendel was an Austrian monk who is often called the "father of genetics" for his study of the inheritance of traits in pea plants.
1. Between 1856 and 1863 Mendel cultivated and tested some 28,000 pea plants.
2. He was the first person to predict how traits are transferred from one generation to the next.
3. He studied only one trait at a time to control variables, analyzed data mathematically.
Important Genetics Terminology
heredity - the passing on of characteristics from parents to offspring
genetics - the branch of biology that deals with heredity
traits - a genetically determined characteristic or condition
gametes - sex cells; a reproductive cell having the haploid (half the normal) number of chromosomes
4. female gamete (♀) - egg, haploid or n (1/2 the normal number of chromosomes, 23 in humans)
5. male gamete (♂) - sperm, haploid or n (1/2 the normal number of chromosomes, 23 in humans)
fertilization - the uniting of ♀ and ♂ gametes
pollination - in anthophytes (flowering plants), the process of transfer of pollen grains from the anther (♂) to the stigma (♀)
Mendel's Monohybrid Crosses
What is a monohybrid cross?
It is a cross between two genetically identical individuals.
Mendel crossed:
purple flowered plant x white flowered plant original parents or P1
he got:
all purple flowered plants first offspring or F1
(F stands for filial, son or daughter)
next he crossed:
F1 (purple flowers) X F1 (purple flowers) F1
he got:
3 purple flowered plants: 1 white flowered plant second offspring or F2
What are Mendel's four “Rules or Laws”?
The rule of unit factor - each organism has two factors for each of its traits
6. We now know these factors are genes located on the chromosomes.
7. These different gene forms are called alleles.
8. Alleles are located in different copies of a chromosome; one from ♂ parent, one from ♀ parent.
The rule of dominance - only one trait was visible in the F1 generation, the dominant trait
9. The dominant trait is the visible or observable trait.
10. The recessive trait is the hidden trait, masked by the dominant trait.
The law of segregation - the two alleles for each trait must separate when gametes are formed
11. A parent passes on at random only one allele for each trait to each offspring
The law of independent assortment - the alleles for one trait behave independently of alleles for other trait during gamete production
Biology 2
Mendel Worksheet Name
Date
Hour
1. Who was Gregor Mendel? (See the “Mendel’s Law” notes.)
2. What were two factors responsible for Mendel’s success? (See the “Mendel’s Law” notes.)
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3. Why was it important for Mendel to count large numbers of plants?
4. What is heredity? (See the “Mendel’s Law” notes.)
5. A trait is a genetically determined characteristic or condition. Describe one physical trait that you probably inherited.
6. What is the branch of biology that deals with heredity? (See the “Mendel’s Law” notes.)
7. What are gametes? What gamete do you produce?
8. Why are gametes described as being haploid? (See the “Mendel’s Law” notes.)
9. What is the diploid number of chromosomes in human cells? (See the “Mendel’s Law” notes.)
10. Garden pea plants reproduce s _ _ _ _ _ _ _. Both male and female gametes are in the same f _ _ _ _ _. The male gamete is the p _ _ _ _ _ g _ _ _ _, whereas the female gamete is in the o _ _ _ _. (See page 286.)
11. What is fertilization?
12. What is pollination? (See the “Mendel’s Law” notes.)
13. What happens to the ovule after it is fertilized? (See page 286.)
14. Explain how Mendel cross-pollinated the pea plants. (See Figure 12.1, on page 287.)
15. What is a monohybrid cross? (See the “Mendel’s Law” notes.)
16. What happened when Mendel crossed a purple flowered pea plant with a white flowered plant? (See the “Mendel’s Law” notes.)
17. What happened when the purple flowered pea plants were allowed to self fertilize? (See the “Mendel’s Law” notes.)
18. What are Mendel's four “Rules or Laws”? Briefly describe each rule or law.
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19. Describe these terms:
gene –
chromosome –
allele -
dominant trait -
recessive trait -
20. Draw and label a homologous pair of chromosomes showing the alleles for purple and white flowers. (See the “Mendel’s Law” notes.)
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