8/31/2018. Lesson 1 (What is Heredity?) Cells and Heredity. 8 th Grade. the passing of physical characteristics from parents to offspring.

Transcription

1 Lesson 1 (Wha is Herediy?) Cells and Herediy Chaper 3: Geneics he Science of Herediy 8 h Grade Herediy rai Geneics he scienific sudy of herediy. Mendel he passing of physical characerisics from parens o offspring. a characerisic ha an organism can pass on o is offspring hrough is genes on is chromosomes. Ausrian monk who was he firs o show he inheriance of rais hrough his work wih pea plans (ofen called he Faher of Geneics ) Purebred Ferilizaion Cross he offspring of many generaions ha always have he same rais as he parens Mendel made sure o sar his experimens wih purebred plans so he could be sure of his resuls. he joining of sperm from a male wih he egg of a female organism. All rais in any organism are decided a ferilizaion. a conrolled maing beween a male and female organism Pure all (crossed wih) Seeds Seeds X X planed planed Mendel s Experimens: Pure shor P generaion (parens) F 1 generaion (firs generaion) All plans were all. Shor rai seemed o disappear. hese plans were allowed o cross wih each oher. Mendel saw his same rend wih all he oher rais he esed. (seed color, flower color, ec.) F 2 generaion (second generaion) Abou ¾ were all, and ¼ of hem were shor. Shor rai reappeared. Mendel s Conclusions: Some facors (or ses of informaion) are responsible for he inheriance of rais. hese facors ha conrol each rai exis in pairs. he female conribues one facor, and he male conribues he oher "facor. One facor in a pair can mask or cover up he oher facor o make i seem o disappear. (allness masked shorness in one of his sudies.) gene a segmen of DNA on a chromosome ha conains informaion o decide a rai. Organisms have wo genes for each rai, locaed on wo maching chromosomes. (Genes occur in pairs because chromosomes are in pairs.) We have wo genes for earlobe shape, wo for hair exure, and so on. alleles he differen forms of a gene Each organism inheris wo alleles for each rai from is parens one allele from he moher (in he egg), and one allele from he faher (in he sperm). You migh have one allele for blue eyes (from Mom), and one allele for green eyes (from Dad). 1

2 Dominan allele Recessive allele an allele whose rai always shows up when his allele is presen A dominan allele will cover up, or mask anoher rai. an allele whose rai is masked (hidden, or covered up) when he dominan allele is presen. A rai conrolled by a recessive allele will show up only when an organism does no have he dominan allele. A person may have 2 dominan alleles for eye color (say blue). Eyes will be blue. OR He/she may have 2 recessive alleles for eye color (say brown). Eyes will be brown. OR He/she may have one dominan (blue) and one recessive (brown) allele for eye color. Eyes will be blue because blue is dominan over brown. All oher rais work he same way. Human Chromosomes hybrid an organism ha has wo differen alleles for a rai (one dominan and one recessive allele) Symbols for Alleles: 1. capial leer represens a dominan allele 2. lowercase leer represens a recessive allele 3. he leer seleced usually represens he dominan rai. If all is he dominan rai and shor is he recessive rai: = all = shor when a plan has 2 recessive alleles (plan will be shor) when a plan has 2 dominan alleles (plan will be all) when a plan has 1 dominan and 1 recessive allele (plan will be all) If blue eyes is dominan over green eyes: B = blue eye allele b = green eye allele BB will have blue eyes bb will have green eyes Bb will have blue eyes 2

3 Female s alleles Heerozygous Examples: Rr, Bb,, ec. Homozygous Examples: RR, bb,, rr, ec. Pure dominan Pure recessive having wo differen alleles for a rai (one dominan, and one recessive allele) Hybrids are heerozygous. having wo of he same alleles for a rai (wo dominan, or wo recessive alleles) having wo dominan alleles for a rai (BB, RR,, ec.) having wo recessive alleles for a rai (bb, rr,, ec.) Probabiliy Lesson 2 (Probabiliy and Herediy) a number ha describes how likely somehing will happen. Probabiliy predics wha is likely o happen, no wha will acually happen. he probabiliy ha a coin oss will be ails is 1 in 2.( or ½ or 50%) Ou of 100 osses you would expec 50 heads, 50 ails (You may no acually ge ha hough.) male female Male can donae eiher (sperm) Female can donae eiher (egg) Punne square a char ha shows all he possible combinaions of alleles ha can resul from a geneic cross hey are used o deermine he probabiliy (or likelihood) of a paricular oucome in a cross. Genoype an organism s allele combinaions (geneic makeup) possible combinaions a ferilizaion Phenoype an organism s physical appearance, or visible rais because of is genoype Male s alleles = all (dominan) = shor (recessive) Each offspring has a 75% chance of being all Each offspring has a 25% chance of being shor If he plan produced 4 seeds, and you planed hem o le hem grow, you would expec o ge 3 all plans and 1 shor plan. Mos rais are he resul of complex paerns of inheriance: 1. Incomplee dominance 2. Codominance 3. Muliple alleles 4. Polygenic inheriance Codominance Lesson 3 (Paerns of Inheriance) a condiion in which neiher of he wo alleles of a gene is dominan or recessive A combinaion of he wo rais shows up in he offspring. Example : A plan wih red flowers is crossed wih a plan wih whie flowers and you ge plans wih whie flowers wih red sreaks in hem (neiher whie, nor red). 3

4 Incomplee Dominance anoher condiion in which neiher of he wo alleles of a gene is dominan or recessive he phenoype resembles a sor of blending of he wo alleles. A plan wih red flowers is crossed wih a plan wih whie flowers and you ge plans wih pink flowers (neiher whie, nor red). Some human rais are conrolled by a single gene ha has several alleles. (muliple alleles) Muliple alleles 3 or more forms of a gene ha code for a rai blood ype ( here are more han 2 blood ypes. ) Some human rais are conrolled by muliple genes. ( More han one gene works ogeher o deermine he rai. ) Polygenic inheriance A person can carry only wo of he alleles because chromosomes are in pairs and each chromosome carries only one allele for each gene. Examples: heigh and skin color occurs when more han one gene affecs a rai Many rais are deermined by boh genes and a person s environmen.) Examples: Heigh is influenced by many genes working ogeher, bu die also plays an imporan role. Genes may conrol personaliy, bu so does he person s environmen. Genes may deermine coordinaion and oher skills of a good ahlee, bu so does ha person s environmen ( coaching, pracice, commimen ). hings in he environmen can affec he genes in an organism, such as causing cancers. Cell division allows organisms o: 1. grow 2. repair damaged srucures 3. reproduce Body cells: Lesson 4 ( Chromosomes and Inheriance ) mos numerous ype of cell in your body produce 2 idenical copies of hemselves by miosis conain wice he number of chromosomes as sex cells Examples: muscle cells, bone cells, nerve cells, skin cells, ec. Humans have 46 chromosomes (or 23 pairs) in each body cell. Sex cells reproducive cells in he body Examples: he Cell Cycle Miosis produced by meiosis conain ½ he number of chromosomes as body cells eggs and sperm Humans have 23 chromosomes in each sex cell. he regular sequence of growh and division ha body cells undergo wo new daugher cells are produced from one paren cell. he sage during he cell cycle during which he cell s nucleus divides ino wo nuclei and one se of DNA is disribued ino each daugher cell during he making of new body cells Meiosis he process by which he number of chromosomes is reduced by half o form sex cells (sperm and eggs) Meiosis occurs only in he ovaries of females and he eses of males. 4

5 Why do sex cells need ½ he number of chromosomes? + = egg sperm offspring chromosomes chromosomes chromosomes When sperm and egg unie during ferilizaion, he offspring mus have he correc number of chromosomes in each of is body cells. 5