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Year 10 Science
Genetics
1
Genetics outcomes
This unit will cover:
•
History
•
Chromosomes and genes
•
Genetics problem solving
•
Human inheritance
•
DNA
To gain a satisfactory for this unit:
1.
Keep a careful record of all theory and related activities
2.
Participate in practical work and complete a written record
3.
Complete a research task
4.
Complete a test or exam
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What is genetics?
• Genetics is the study
of heredity
• Animals, plants and
micro-organisms are
studied
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History
• Gregor Mendel – father of genetics
• Monk in Austria in 1856
• Studied peas in the monastery garden
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Mendel’s results
Parent
round pea X wrinkled pea
F1
F1 crossed
F2
all round peas
F1 X F1
3 round : 1 wrinkled
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Mendel’s conclusions
• Round is dominant to wrinkled in peas
• Yellow is dominant to green peas
• A dominant trait masks the effect of a
recessive trait
• Mendel’s scientific work was ignored for
about 40 years
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Chromosomes
• Are long thread like
structures found in
the nucleus
• Made of a chemical
called DNA
• Deoxyribonucleic acid
• DNA is coiled tightly
inside a cell
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Genes
• Genes are found on
chromosomes
• Genes code for
particular traits
• Many thousands of
genes are found on
each chromosome
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Homologous chromosomes
• 2 copies of each
chromosome in each
body cell
• 2 copies of each gene
in each cell
• Humans have 46
chromosomes in each
body cell
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Chromosomes, genes and alleles
10
Haploid and diploid cells
• Diploid cells have 2 copies of each chromosome
eg body cells
• Haploid cells have 1 copy of each chromosome
eg gametes (egg and sperm)
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Human chromosomes
• Humans have 46
chromosomes in
every body cell
• 23 chromosomes in
every sperm and egg
egg
23
X
sperm
23
zygote
46
New individual
46
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Mitosis
• The process of cell
division to make new
body cells
• replaces old and
damaged cells
• 2n
2n
• 46
46
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Meiosis
• Formation of eggs in
ovary and sperm in
ovary and testes
• Forms haploid cells
• 2n
n
• Human chromosomes
46
23 in egg or
sperm
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Genotype and phenotype
Let B = brown eyes, b = blue eyes
B is dominant to b
• Every individual has 2 copies of each gene
• The genotype of an individual is its genetic
makeup eg BB or Bb or bb
• The phenotype of an individual is its outward
appearance eg blue eyes or brown eyes
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Homozygous and heterozygous
• An allele is the alternative forms of a gene
eg B or b
• Homozygous individuals have the same
allele on both chromosomes eg BB or bb
• Heterozygous individuals have different
alleles on both chromosomes eg Bb
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Homozygous X homozygous
Let B = brown eyes, b = blue eyes
B is dominant to b
P phenotype brown eyes X blue eyes
P genotype
BB
X bb
Gametes
B
b
F1 genotype
Bb
F1 phenotype
All brown eyes
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Heterozygous X homozygous
P phenotype brown eyes X blue eyes
P genotype
Bb
X bb
Gametes
B, b
b
F1 genotype
½Bb, ½bb
F1 phenotype ½brown eyes, ½blue eyes
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Heterozygous X heterozygous
P phenotype brown eyes X brown eyes
P genotype
Bb
X Bb
Gametes
B, b
B, b
gametes
B
b
F1 genotype
F1 phenotype
B
b
BB Bb
Bb bb
¼BB , ½Bb, ¼ bb
¾brown eyes, ¼ blue eyes
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Co-dominance
• In co-dominance, the phenotype of the
heterozygote is a combination of the
homozygous individuals
• Roan cattle
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Incomplete dominance
• The heterozygote is
intermediate between
the two homozygous
organisms
• Snap dragons colours
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