mendel, genes, and inheritance ( 멘델, 유전자 그리고 유전 ) chapter 12
TRANSCRIPT
Mendel, Genes, and Inheritance ( 멘델 , 유전자 그리고 유전 )
Chapter 12
털 색깔의 유전적 변이를 보이는 쥐
그림 12.1. 낫 모양 세포 빈혈증 환자의 적혈구
12.1 The Beginnings of Genetics: Mendel’s Garden Peas ( 완두콩 )
Mendel chose true-breeding ( 순계 ) garden peas for his experiments
Mendel first worked with single-character crosses ( 단인자교배 ; 단성교배 )
Mendel’s single-character crosses led him to propose the principle of segregation ( 분리의 법칙 )
Mendel could predict both classes and proportions of offspring ( 자손의 분류와 비율 )from his hypotheses
12.1 (cont.)
Mendel used a testcross ( 검정교배 ) to check the validity of his hypotheses
Mendel tested the independence ( 독립성 ) of different genes in crosses
Mendel’s research founded the field of genetics
Sutton’s chromosome theory ( 염색체설 ) of inheritance related Mendel’s genes to chromosomes
Blending Theory ( 혼합가설 ) of Inheritance
Popular belief until about 1900 • Hereditary traits blend evenly in offspring through
mixing of parents’ blood
Does not explain some observations:• Extremes do not gradually disappear• Offspring sometimes have different traits than
either parent
Gregor Mendel
Founder of genetics
Augustinian monk (1822-1884)
First to use scientific method to study inheritance
Pea Experiments
Garden pea (Pisum sativum)• Easy to grow• Clearly defined characters ( 특성 ) or traits (
형질 )• True-breeding ( 순계 ) varieties• Self-fertilized plants (same trait each generation)
• Easy to cross ( 교배 ; 교잡 )• Cross-pollination ( 타가수분 ) between parents
그림 12.3. 멘델의 실험에 사용된 완두콩 .
그림 12.4. 멘델의 7 가지 특성을 대상으로 한 교배 결과
Single-Character Crosses ( 단성교배 )
P generation (Parents)• Each pea produced contains an embryo
F1 generation (Filial)
• First generation
F2 generation
• Second generation
Flower Color Cross
P generation• Purple flowers crossed with white flowers
F1 generation
• All F1 seeds formed purple flowers
• Purple flower offspring crossed
F2 generation
• Purple flowers (75%)• White flowers reappeared (25%)
Mendel’s First Hypothesis
Genes for genetic characters occur in pairs • One gene inherited from each parent• Alleles are different versions of a gene
Diploid: two copies of each gene
Mendel’s Second Hypothesis
If two alleles of a gene are different, one allele is dominant over the other• Dominant allele is expressed• Recessive allele is masked
Recessive alleles only expressed when two copies of the allele present
Mendel’s Third Hypothesis
Two alleles of a gene segregate (separate) and enter gametes singly• Half the gametes carry one allele, half carry the
other allele (haploid)• Principle of Segregation
Two gametes fuse to produce a zygote that contains two alleles (diploid)
Terminology
Homozygous• Both alleles the same• PP (dominant)• pp (recessive)
Heterozygous• Two different alleles• Pp
그림 12.5. 완두콩의 꽃 색깔에서의 분리의 법칙
Terminology
Genotype ( 유전자형 )• Genetic constitution ( 유전적 구성 ) of an
organism• PP, Pp, pp
Phenotype ( 표현형 )• Outward appearance• Purple flowers, white flowers
Product Rule in Probability ( 확률의 곱셈법칙 )
Probability of two independent events occurring in succession ( 연속적으로 발생하는 두 개의 독립적 사건의 확률 )• Individual probabilities multiplied
Coin flip probabilities• Heads ( 앞면 ) = ½• Tails ( 뒷면 ) = ½• Two heads = ½ × ½ = ¼• Two tails = ½ × ½ = ¼
그림 12.6. 확률의 법칙들
Sum Rule in Probability ( 확률의 덧셈법칙 )
Probability of two different events producing the same outcome ( 같은 결과를 얻는 두 가지 다른 사건들의 확률 )• Individual probabilities added
Probability of a heads and a tails in two tosses:• First possibility: heads then tails • Heads = ½, Tails = ½ (½ × ½ = ¼)
• Second possibility: tails then heads • Tails = ½, Heads = ½ (½ × ½ = ¼)
• Total probability: ¼ + ¼ = ½
Probability in Mendel’s Crosses
Heterozygous cross (Pp × Pp)• Genotype probabilities• PP zygote = ½ × ½ = ¼• pp zygote = ½ × ½ = ¼• Pp zygote = ¼ + ¼ = ½
• Phenotype probabilities• Purple flowers = PP + Pp = ¼ + ½ = ¾• White flowers = pp = ¼
그림 12.7. 퍼넷 사각형으로 유전적 교배에서의 자손들과 그 비율을 예측 .
그림 12.8. 검정교배로 유전자형을 확인
Mendel’s Fourth Hypothesis
Alleles of genes that govern two different characters segregate independently during formation of gametes• Principle of Independent Assortment ( 독립의
법칙 )
Due to independent assortment ( 독립적 분리 ) during meiosis
Dihybrid Cross (1)
Pea shape Pea color• R = round Y = yellow• r = wrinkled y = green
P generation: RR YY × rr yy• RR YY parent produces R y gametes• rr yy parent produces r y gametes
F1 generation• All offspring Rr Yy genotype• All offspring round smooth phenotype
Dihybrid Cross (2)
Two heterozygotes crossed
P generation: Rr Yy × Rr Yy• Rr Yy parents produce 4 kinds of gametes• ¼ R Y, ¼ R y, ¼ r Y, ¼ r y
F1 generation• Offspring have four phenotypes• 9/16 = round yellow• 3/16 = wrinkled yellow• 3/16 = round green• 1/16 = wrinkled green
} 9:3:3:1 ratio
그림 12.9. 독립적 분리로 조합되는 종자 모양과 종자 색깔 형질
Dihybrid Testcross [ 양성 ( 이인자 ) 검정교배 ]
P Generation• Rr Yy × rr yy
F1 Generation
• ¼ = round yellow• ¼ = round green• ¼ = wrinkled yellow• ¼ = wrinkled green
} 1:1:1:1 ratio
Mendel’s Legacy ( 유산 )
Mendel’s results presented in 1866• Only known locally
Mendel died in 1884
Work was rediscovered in early 1900s
Mendel is considered the founder of genetics
Chromosome Theory of Inheritance
Walter Sutton (1903) noted similarities between inheritance of genes and behavior of chromosomes in meiosis and fertilization• Chromosomes occur in pairs in diploid organisms• Chromosomes of each pair are separated and
delivered singly to gametes• Independent assortment of chromosomes• One chromosome of each pair is derived from the
male parent; one from the female parent
그림 12.10. 염색체와 유전자의 행동양상은 서로 평행적 .
그림 12.11. 상동염색체의 특정 위치에 존재하는 염색체 좌(locus)
그림 12.12. 멘델의 유전법칙을 따르는 사람의 유전형질들 .
12.2 Later Modifications and Additions to Mendel’s Hypotheses ( 멘델의 가설에 대한 수정과 추가 )
In incomplete dominance ( 불완전 우성 ), dominant alleles do not completely mask recessive alleles
In codominance [ 공 ( 동 ) 우성 ], the effects of different alleles are equally detectable in heterozygotes
In epistasis ( 상위 ), genes interact, with the activity of one gene influencing the activity of another gene
12.2 (cont.)
In polygenic inheritance ( 다인자유전 ), a character is controlled by the common effects of several genes
In pleiotropy ( 다면발현 ), two or more characters are affected by a single gene
Incomplete Dominance ( 불완전 우성 )
Some or all alleles of gene are neither completely dominant nor recessive
Heterozygote phenotype• Different from either homozygote phenotype
그림 12.13. 금어초 (snapdragon) 꽃 색깔의 불완전 우성
Incomplete Dominance in Human Traits Sickle-cell disease• Homozygote recessive has sickle-cell disease• Heterozygote has milder sickle-cell trait
Familial hypercholesterolemia ( 가계성 과콜레스테롤증 )• Homozygote has severe form of disease• Heterozygote has mild form of disease
Tay-Sachs disease ( 테이 - 작스병 )• Homozygote has serious symptoms• Heterozygote has no symptoms but has
detectable biochemical effects
Codominance
Different alleles of gene have equal effects in heterozygotes• Both alleles expressed
Human M, MN, and N blood types• LMLM = M glycoprotein present; blood type M• LNLN = N glycoprotein present; blood type N• LMLN = both glycoproteins present; blood type MN
Similar inheritance to incomplete dominance
Multiple Alleles
More than three alleles for a gene• Found among all individuals in a population• Diploid individuals only have two of the alleles
Phenotype depends on relationship between different pairs of alleles• Still follows Mendel’s principles • 그림 12.14 ( 없음 ; 교과서 참조 )
Human ABO Blood Group
Antigens • Glycoproteins on surface of red blood cells• IA allele produces A antigen (dominant)• IB allele produces B antigen (dominant)• i allele produces neither A nor B (recessive)
Blood types (phenotypes)• IAIA or IAi = type A blood• IBIB or IBi = type B blood• ii = type O blood• IAIB = type AB blood
Human ABO Blood Group
Immune system produces antibodies against antigens not found on its own red blood cells
그림 12.15. 사람 ABO 혈액군의 혈액형 유전 .
Epistasis
Genes interact• Allele of one locus inhibits or masks effects of
allele at a different locus • Some expected phenotypes do not appear
among offspring
Labrador Retrievers ( 래브라도 리트리버 )
Melanin pigment gene• B allele: black fur color (dominant)• b allele: brown fur color (recessive)
Pigment deposition gene• E allele: pigment deposition normal (dominant)• e allele: pigment deposition blocked (recessive)
Phenotypes• Black fur: BB EE, BB Ee, Bb EE, Bb Ee• Brown fur: bb EE, bb Ee• Yellow fur: BB ee, Bb ee, bb ee
그림 12.16. 래브라도 털 색깔의 상위 유전
Polygenic Inheritance
Several genes at different loci interact to control the same character• Produces continuous variation
Phenotypic distribution: Bell-shaped curve
Often modified by environmental effects
그림 12.17. 다인자유전에 의한 키의 연속적인 변이 .
Pleiotropy
One gene affects more than one character
Sickle-cell disease• Recessive allele affects hemoglobin structure and
function• Leads to blood vessel ( 혈관 ) damage• Damages many tissues, organs, and functions• Many different symptoms result
그림 12.18. 낫세포 빈혈증의 다면발현 효과